As corny as the old adage is, in most instances it's true: There's no replacement for displacement. And these days, with the availability of stout mail-order crate engines, the cost of buying a brutish big-block is now within the budget of many gearheads. Case in point: GM Performance Parts' burly 502/502 big-block (PN 12371171) that can be had for about $6,000. In the Sept. '97 "Crate Engine Shootout!" story we tested the 502/502 and were giddy to see 513 hp and 555.5 lb-ft of torque. However, even though a crate engine's price may be lower than what you'd spend building a similarly performing mill, we wondered what hassle and expense would be required to shoehorn such a fat-block into a traditional musclecar. We'd always heard that a big-block Chevy was an easy swap into a small-block car--but is it true? With the 502 and an A-body on hand, we decided to find out for ourselves and share with you the details and the costs. As usual, CC's much-abused Cheap Street Chevelle was the guinea pig, but much of the info will apply to most '68-'72 GM A-bodies or GM fullsize barges. After jerking the small-block and test-fitting the 502, the first thing we learned was that the 502/502 comes with a six-quart truck-style oil pan that interferes with the engine bay in our '70 Chevelle. We replaced it with a special Milodon oil pan that merges the correct old-car-shape to fit the chassis with the new-car-type pan rails that fit the new Gen 5/Gen 6 big-blocks and their one-piece rear-main seals and revised gaskets. The Milodon oil pan's unique design has a large seven-quart oil capacity for reliable oiling during racing yet is a low-profile design to avoid ground-scraping woes. Often, you can reuse the 502's stock one-piece rubber oil pan gasket, but if not, companies such as Fel-Pro offer a gasket under PN OS34407R. The Milodon oil pan (PN 30955) requires a special oil pick-up tube assembly (PN 18301) to be properly oriented within the new oil pan's sump area.The Milodon oil pan (PN 30955) requires a special oil pick-up tube assembly (PN 18301) to If your '68-'72 GM A-body originally came with a 350 small-block, you can retain the original engine frame mounts. If it had a 307 V-8, you'll need to switch to 350/396/454-style engine frame mounts (GM PN 3980711 left, 3980712 right), which should also work on non-Chevy A-bodies. On the engine side you'll need to upgrade to new GM big-block engine motor mounts (PN 03962748).If your '68-'72 GM A-body originally came with a 350 small-block, you can retain the origi We installed a new Milodon 160-degree-F thermostat and then bolted on a reproduction big-block-style thermostat housing (PN 26016) from OPG. Rather than reusing the crusty old bolts from our small-block, we opted for an ARP big-block bolt kit (PN 535-9501).We installed a new Milodon 160-degree-F thermostat and then bolted on a reproduction big-b The 502/502 comes with an aluminum water pump, but it's designed for Reverse rotation and would require switching to modern-style serpentine belt-type pulleys and brackets that would be a bit pricey. We installed a new Edelbrock long-style aluminum water pump (PN 8851) that accepts traditional early type pulleys, brackets, and hoses.The 502/502 comes with an aluminum water pump, but it's designed for Reverse rotation and New crank and water pump pulleys are available from OPG. We opted for LS6/L78-style deep-groove crank (PN SL39119) and water pump (PN SL39414) pulleys to avoid any high rpm belt-throwing mishaps. A 15450 fan belt fit perfectly.New crank and water pump pulleys are available from OPG. We opted for LS6/L78-style deep-g The small-block alternator brackets won't work with the big-block, so we installed OPG's big-block alternator bracket set (PN FL8502). Our old alternator already had an aftermarket deep-groove aluminum pulley, but if you want one of OPG's deep-groove pulleys, order PN SL39120.The small-block alternator brackets won't work with the big-block, so we installed OPG's b We found out the hard way that small- and big-block (right) power-steering pumps looked the same, but had slightly different lines exiting the back. To use OPG's factory-type big-block brackets (PN SFL8504) we also needed to upgrade to a new (expensive, ouch!) big-block power-steering pump (PN TRI6165) from OPG.We found out the hard way that small- and big-block (right) power-steering pumps looked th A big-block (including Gen 5/Gen 6 big-blocks) fits into the engine bay of a GM A-body without much hassle, but getting headers to fit was the real trick. Hedman offers two varieties of 13/4-inch headers (full length and 3/4-length) that work great. We opted for Hedman's 3/4-length headers (PN 68610) because they're easier to install, tuck up tighter, and provide added ground clearance. The headers can also be ordered with a trick hi-temp coating for an added price, but gaskets and bolts were included free. Before installing the engine, we test fit the headers to make sure they cleared the gear-reduction starter (included with the 502), motor mounts, and oil pan. If you prefer, stock-type manifolds are available from OPG.A big-block (including Gen 5/Gen 6 big-blocks) fits into the engine bay of a GM A-body wit We learned that the passenger-side header must be installed from underneath the car. Have one guy slip the headers in from below while another installs the gasket and bolts (included) from above.We learned that the passenger-side header must be installed from underneath the car. 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