318 magnum VS 318 roller VS older 318 gas mileage

I pulled the 273 in my 65 Cuda about 1 1/2 years ago and swapped in a 2001 Magnum 5.2. Best thing I ever did! I did it for the same reasons you are thinking of it - too much $$ to rebuild the old one.

The block is pretty much identical to the old one. From the old engine I reused the timing case, water pump and pulley assemblies, motor mounts, valve covers, distributor and exhaust manifolds.

The new motor had a mini starter so I used it. Nice added bonus!

I didn't use the old intake manifold. The bolt holes are angled differently and it's somewhat restrictive.

Your old oil pan won't work. The mains are different size on the the Magnum but that's just a minor problem.

I did very little internal work to the engine. I replaced the oil pump and screen, rod bearings and main seals.

Mine is a 4 speed car with 3.90 gears and i get 15-16 mpg around town. I plan on swapping in a set of 3.23s that I have to make it cruise just a bit easier.

I'm not a 'speed' guy but this thing has WAY more power than the 273. It's reliable and runs great.

If you want more details on the swap, I'm happy to help however I can.