hello man, saw ur post in members gallery, people get a bit pissed off about posting without pics so i started a new one!
an rs125 engine wudn't go into an rs50, not without a lot of work anyway. the drive is on the other side on the rs125, and the engine acts as a spacer to the swingarm, which is about 2 inchs bigger on the rs125 (i thought about fitting an rs125 swingarm to my rs50)
you can either fit a 400cc+ like hybrid (think thats rite?) or,
You can get someone in the uk (stu ) to find you an rs125, drain and strip it, and send it over in a crate, i'v seen an artical on this forum about shipping from italy to usa before, will try and find it.
the rs125 is a totally new bike to the rs50, my rs50 is highly moddified and it is nothing like the power of an rs125, plus the 125 looks like a real bike!
will look for that artical