This is a comparison of the...
This is a comparison of the standard-style small-block cam nose (left) versus the '87-and-later factory hydraulic roller cam arrangement (right). Note that the factory hydraulic roller uses a step. This stepped nose with a smaller bolt circle must match the cam gear. That means there are two different cam gears for the small-block Chevy depending upon the cam chosen.
Roller Warning
One area where you must be careful with production-based small-block Chevy hydraulic roller lifters is with high-lift camshafts. According to Crane's Director of Valvetrain Research and Development, Mark Campbell, valve lifts of more than 0.530 inch at the valve with a 1.5:1 rocker can allow the lifter to fall deep enough into the lifter bore (because of the lobe's small base circle) that the steel retainer can lose its grip on the lifter body. This allows the lifter to spin in the bore and destroy the camshaft. In checking a few cam catalogs, it is possible to order a hydraulic roller camshaft with enough lobe lift (in excess of 0.354 inch) to create this situation, so just be careful. This is why Crane created a long-travel hydraulic roller lifter that will allow you to run a high-lift hydraulic roller cam with the stock lifter configuration. These eliminate the problem but are also much more expensive than OE replacement lifters. Another solution would be to run a 1.6:1 rocker ratio with a reduced lobe lift cam to accomplish more valve lift.
Roller-Cammed Ford 5.0s
Ford has been building 5.0L small-blocks with roller cams since 1984 in fullsize cars (although many others are still flat-tappet motors, so you have to be careful). In the Mustang, the first roller cams appeared in 1985 Mustang and continued through the '95 pushrod motors. One advantage of an '85-'92 Mustang engine is that the pistons are forged, making these an excellent performance engine platform. These engines also make great baselines for a stroker 331- or 347ci small-block, which can be built using the stock hydraulic roller lifter configuration to keep the price down. As you can see from the accompanying Ford parts list, Ford's price on a brand-new set of hydraulic roller lifters is a very affordable $125 compared to as much as $480 for aftermarket lifters.
The stock hydraulic roller...
The stock hydraulic roller cams used in Ford 5.0L engines retain the lifters in a similar fashion to the small-block Chevy, with steel retainers that slip over flats on the hydraulic roller lifter. The retainers are held in place with a stamped-steel spider bolted to the cylinder block's lifter valley.
Let's play out a low-budget 5.0L engine scenario here. Yank an '88 5.0L motor out of a boneyard Mustang GT and discard the EFI manifold. We'll assume the engine is in good shape. Do a simple ring-and-bearing rebuild on the short-block and the forged pistons to make sure the engine is well sealed up. Add a gasket set (make sure and get the one-piece oil pan gasket) and a new oil pump, and the short-block is ready. Next, dial in a performance hydraulic roller cam. A good choice would be something around 224 degrees at 0.050-inch tappet lift with around 0.540-inch lift, and plan on reusing the stock hydraulic roller lifters and factory retaining assembly. Then tune up the heads with a valve job, screw-in studs, guideplates, and a good set of rocker arms and valvesprings; top it all off with a set of headers and a dual-plane intake manifold; and you've got a solid 5.0L that will make around 325 hp and 350 lb-ft of torque. If you find a used intake and budget headers, it's entirely possible to build this entire engine for under $1,500.
It's also possible to upgrade the '95-and-later 351W engine with factory-style hydraulic roller lifters and retainer assembly. These engines have the bosses cast into the block, which makes the conversion much easier. Comp Cams sells a retrofit roller lifter kit (PN 31-1000 and 31-1001) with a stock-type spider and retainers that can be added to certain of these blocks. However, this will require the proper base circle hydraulic roller cam to ensure that the roller lifters don't travel beyond the vertical capacity of the lifter bores.