Welcome to the board "mikeakageoff", I was a bit confused by the question because I wasn't sure what a fornt end was!

Seriously there are a number of guys on here who will know the answer to your front end question.

Just for the record your old 907 is still looking good in my garage, I hope your replacement one is on the road soon!!!

ooh! I was all excited and thought I'd got a sensible answer to my question, ah well...

Which 851 front end do you want to use?
The first year 851 used the Marzocchi M1R forks and had 16" wheels, which was almost same as the Paso. However, the travel was really short, like 105mm or something like that, so it may lower your front end, which will quicken you steering.The Paso had 135mm travel. The triple clamps also had about 3mm more offset, which will again quicken the steering. They also had clipon handlebars. Its a pretty rare front end to find, and you may not like it when you get it.

From the second year on, they used the upside down forks and a 17" wheel. I have no idea what the travel was, or the length of the forks, but measuring them would be your best bet.

A cheaper, easier swap might be getting a front end from an SS or Monster. Much more common, hence, cheaper.

Phil
1990 Sport