I believe it's a matter of want.
He already has the engine, and wants to build it himself rather than simply going crate.
Can't say I blame him, hard to learn about engine internal parts and how to assemble, work on, trouble shoot and understand the how and why without getting dirty or by dropping a crate in.
He has a lot of body and paint experience and wants to learn engines and other mechanical workings so he can have more experience and knowledge

And besides.. if he got the crate engine.. my wife would chop off my head when I got the 429 for myself from him
I'm kinda attached to it!