Oil System
From the factory, the 5.7 and 6.1 engines in passenger cars have front-sump pans. The truck applications are rear sump. But none of the factory pans will clear any stock K-frame and steering linkage in any classic Mopar. Bottom line--you'll need a custom pan. Milodon makes a midsump pan that will clear the factory K-frame and drag link. Bouchillon Performance makes several pans to fit the stock stuff as well as aftermarket K-frames and rack-and-pinion steering, and Charlie's Oil Pans will make you a pan in any configuration you want. Of course, you'll need to buy an oil pickup tube and dipstick to match the new pan.
Oil filter fitment is also a problem. Most new Hemi engines mount the filter to a boss on the passenger-side front of the block that would interfere with the factory K-frame. Many people recommend installing a block-off plate on the engine and running a remote-mount oil filter. LaPaglia discovered that the Dodge Durango uses an adapter that mounts its oil filter at a 45-degree angle to the block, and that gave him just enough clearance to mount a filter to the block using factory parts. Beware, though, that the oil filter itself is too big. You can unscrew it from the adapter, but it will hit the K-frame before you can pull it out, and you'll have to jack up the engine to remove it. LaPaglia discovered that a Fram PH3512 filter fits the boss and is short enough to fit without breaking out the engine hoist every time you change the oil.
On LaPaglia's car, there is...
On LaPaglia's car, there is little room between the bottom of the engine block and the factory K-frame. The stock passenger-car oil pan would never fit. Bouchillon's midsump pan clears the K-frame and steering linkage.
Cooling System
The new Hemi water pump has coolant in the inlet and outlet fittings on the passenger side of the block. You, therefore, need a radiator with matching fittings on the passenger side. LaPaglia found a Ron Davis radiator that fit his Challenger and the new water pump. You'll also need to spend some time finding properly bent radiator and heater hoses. Be sure to budget for a good pair of fans, too. The 6.1 engines have no provisions for mounting a mechanical fan, so you have to use electric fans. Some of the 5.7 engines, mostly from fullsize pickups, can use a mechanical fan, though. LaPaglia uses a pair of Spal fans to keep coolant temperatures in check. Bouchillon sells a complete radiator and fan kit for any classic Mopar.
Fuel System
As equipped from the factory, the new Hemi is a returnless system--high-pressure fuel is pumped to the engine by a pulse-width-modulated fuel pump, but there is no return line back to the tank. Though you can run an external fuel pump, an in-tank pump makes for a cleaner install. Street & Performance sells a return-type regulator and fuel filter assembly that mounts close to the tank, and you can alter your stock tank with a fitting to accept the return line. The advantage to this is you don't need to alter or replace the factory fuel rail to accept a regulator and return line fitting and plumb a return fuel line. Bouchillon Performance sells a similar kit that uses an in-line pump and a fuel filter that doubles as a pressure regulator.
The Durango angled oil filter...
The Durango angled oil filter adapter keeps you from having to plumb in a remote oil filter.
LaPaglia recommends replacing your car's original gas tank with a baffled tank specifically designed for fuel injection. He did not and therefore has fuel starvation issues in hard cornering situations when his tank is less than half full. Unbaffled, fuel slosh in the tank can uncover the fuel pickup.
Accessories
Your old accessories won't fit the new engine, so you'll need the new engine's alternator, water pump, power steering pump, and A/C compressor if you want air conditioning. All the engine-driven accessories mount to the front timing cover, and the new Hemis have two different covers: one for the trucks and one for the passenger cars. In most applications, the passenger-car timing cover is the better choice.
Air Conditioning
It is possible to keep or even add air conditioning when swapping in a new Hemi, but you'll have to use the new engine's compressor. That compressor will fit your engine compartment, but you may need to notch the K-frame for clearance. You will also need to dimple the No. 1 cylinder's header tube and grind a mounting tab off the back of the compressor. LaPaglia wrapped his lines with heat-resistant insulation--the headers can't get any closer than this. Also, the new compressor's fittings are different from the threads on the older car's lines. You'll need adapters to fit the old lines to the new compressor.
 Use a shorter-than-stock filter...  Use a shorter-than-stock filter if you want to be able to remove it easily. |  The new Hemi cooling system...  The new Hemi cooling system is radically different from A, B, RB, and 426 Hemi engines. |  You can mount an A/ C compressor,...  You can mount an A/ C compressor, but it is a really tight fit. |