318 Duster Rebuild - pros and cons of keeping matching numbers

If you can pull heads and replace them you can do the rest. Don't be afraid. If you don't feel comfortable opening a trans I get it but if you can pull it and take it to someone even that will save you a lot. Same with the engine. Pull it you can find a stand on CL or marketplace cheap, (or borrow one from a buddy) and clean up the engine yourself, if you can pull heads you can replace gaskets. You'd be saving yourself a ton. The cost to buy some basic tools would be cheaper than having it done for you you still have the tools.