Hey Peyote (most young kids may not know about the psychedelic drug), I live in Corpus Christi and you're absolutely correct...no Mopar parts for hundreds of miles. When you can find them they cost a small fortune. That's why I stuck a Chevy 2004R in my Barracuda, total cost $1850. I did all the work myself except for the tranny overhaul. The 2004R core was only $25. Since Chevy rear ends are also abundant around here I installed a Chevy 10 bolt posi in the Cuda with 12 bolt axles and 390 gears. I got beat up pretty good here on FABO for using Chevy parts on a Mopar but I saved tons of money and the 10 bolt was just sitting in my garage anyway. I have a extra 904 sitting in my garage that you can have for $75. I also have 2 318 blocks. One is a short block ready to go and the other is a bare block. I also have the original high compression heads that came off my '69 Barracuda (9.2:1 CR) sitting on the shelf. Other various Mopar parts. Lots of 340 and 360 magnum small block exhaust manifolds.
The 318 engines, depending on the year, came with pistons sunk down in the hole. '69 pistons were the tallest. My pistons sit .039" down in the hole, some are as deep as .100" (or more) so be aware of what year engine you buy as it will determine the compression.
Treblig
Good luck with your build