Right on. Well if you can be a plumber you can figure out how to slap in a Lifan 125 into a 30yr old HOnda! Check this bike out. It's a super old Honda S90. I used to ride one of these to high school every now and then back in 1993! The "friend" that bought it from me swore he wasn't going to sell it to anyone else and that he would sell it back to me someday. Yeah right... he sold that super rare Honda to someone else immediately to make a buck!! Anyway this dude on Youtube put a LIfan 125 into the Honda 90 and it's a 6V bike to begin with. It's not that hard at all. Sounds like you got it made on that engine swap. He also said in the comments that there is a HOnda engine group on Yahoo that has all the info diagrammed out. You could look up some more info on that to see if that helps. I might look at that later myself just for kicks.
I'll just post the video in a window here. If you want to read the comments and see the users profile and stuff you can click on the "youtube" emblem to open up another window so you can see all that stuff.