I gave this a quick play last night. The changes made were minor, but it definitely makes things easier. The last demo released was punishingly difficult, which was fine by me; it feels like quite an accomplishment to beat it, but Contra is the only game I would personally ever welcome that kind of difficulty in, and I'm sure it was over the top for most. The final version is fairer and better balanced, and as long as you're careful and attentive you have a shot.
Regarding carting, rather than sacrificing a donor, you may be able to get new parts. It looks like infiniteneslives
doesn't have MMC1 in stock right now, and I could have sworn that bunnyboy sold MMC1 hardware at retrousb.com, but I don't see any carting hardware on his site anymore. It couldn't hurt to shoot them a message, though.