On my Cuda, I went with a 440 since it was an option on the car plus for the 440 are very, very easy to find. Mopar continued to make 440s even until the late-seventies for their vans and trucks. They were also one of the most popular blocks for motor-homes. This means if you need parts they are usually cheap and readily available.

I bought my 6-Pack/forged crank 440 block for $600 and the engine shop had few problems getting it knocked back into shape. The sky is the limit with these engines with the right heads, exhaust, fuel system, etc.

Want to hook up electronic ignition and EFI? No problem.