I did exactly as you have described, I purchased a motor and tranny from Cleveland, then stuffed it all in a 72 Demon. I did a build thread here on FABO. For me it worked out well and was very cost effective. Were I to do it again I would probably lean towards doing it the same way. At the time I did it there were not many options available. There may be more now? I dunno? Purchasing it as a whole saved me a lot of headache and time. Send me a PM if you wish and I can provide more details. PS the project is not for the feint hearted!