Re: Im a newb and have way to many questions in the confusing world of motorize bikes
You could squeeze a China girl 2 stroke in that bike, it's been done, but you'll need offset mounts, or a full jackshaft from sickbikeparts.com
As far as pulling 375lbs you plus 80 lb bike plus 75lb gear I think your maybe expecting too much from a small 66cc two stroke
I'd recommend a ezm four stroke, they have one that users the harbor freight 79-99 cc motors. You can also build a 212 cc 4 stroke as some others have done
You'll need a new bike, motor, mount and a drive system. I think you'll be much happier with that than a cheap China Girl in a little mongoose fat bike from Walmart.
You can't fit a high compression head on the 2 stroke inside the dolomite, you can probably get a nice kx60 pipe on there, even a mikuni or dellorto carburetor and hit some serious hp, you can port the cylinder, even get an iron sleeved ported cylinder.
After you spend $1000 on your little two stroke, if still needs oil mixed in every tank, and it's still a vibrating little time bomb.
Sounds like you plan to rack up thousands of miles, that's a job for a four stroke, not a little China girl.