Crate 360 vs DIY Built

so my project 70 Dart will eventually have a 360 under the hood to replace the original /6. I have a 360 engine already from a 77 Cordoba. It turns over but I don't know the condition of the internals, if the block has any damage, ect. it needs a new ignition, exhaust, intake at least. It will likely need a full rebuild.

The direction im goin with for my car is a Pro-tourin style. Full RMS suspension, decent power and torque, good mpg so it can be a daily driver.

I saw in a catalog they have crate Magnum 360's for about $6k. granted I may save a few bucks just rebuilding my current engine, would I be better off with a brand new Dyno tested 0 mile Magnum over a 40 year old LA motor? The Magnum would likely get better mpg over the LA, right?

On top of that, what would you do about the transmission? new or used?

Thoughts? I appreciate the input!