I have never personally skied the J'mos, so I couldn't really give solid advice on the mounting point. However there are plenty of guys on here who have, so you should have no problem finding someone to give you an answer with regards to +/- however much.
But I can help you with the binding situation. In short the FKS/Pivot140 is a far superior binding to the Griffon feature a lot more metal, a lower stand height and better power transmission. However as you yourself pointed out this does come at a price. If you're not willing to drop the £££ on the FKS, perhaps the Axial2 120/PX12 might be your ticket. It features the same FullDrive toe as the FKS 140 but replaces the Pivot heal with the PX heel. The Axial2 120 is a quality binding and up with the STH 12 Driver as the best 12din binding on the market. Take a look of my review of them here: http://aslansskiblog.blogspot.co.uk/2012/08/rossignol-axial2-120-ski-binding-review.html
Hope this helps, if you got any questions about the above or the review feel free to pm me or contact me through the blog, I'll pick it up either way.
Check my blog for updates, reviews and some avi awareness basics: http://aslansskiblog.blogspot.co.uk/
You know you bought the right size if there's more Xs on the label than the door of a porn theatre