I have concerns with some playability / fun factor on the engine. While I realise that the entire point of this mod is to emulate the 64 engine and gameplay, and bring it to a space with more characters and stages to play around with, but why limit ourselves to that? There were a few definite flaws with 64 engine that made it feel a bit clumsy in my opinion, as there were with Melee, but the difference is that when making Project M, the PMDT accepted this fact and kept many of the technical things from Brawl, while not bringing everything over from Melee, notably the bad things. I want this mod to be fun and as awesome as Project M when it releases, but there are a few things that keep me from only playing Smash 64 currently: namely the clumsy grab mechanics with no dash grabs, no air dodges, oddly small window for Z-Cancelling (this isn't a necessity, just something that would be convenient to make easier (perhaps an option in the Rules menu?)), and the obvious lack of extensive content, but that last one won't be a problem eventually.
TL;DR
I don't feel that it would be optimal to just clone the 64 engine, instead, I think you should make a few of its clumsy elements more user-friendly, especially coming from a game like Melee or PM.