[petrolhead611]

I grew up around those nasty little cars, sister had an ex-track Mini 999 that I put back to street legal for her, and my mom had an 850.I raced a Mini Marcos, more about that anon.They are all real puddle jumpers, and they rust even faster than they leak oil.
The power of a 1275 can be hiked right up simply with a Cooper cam +1.5 roller rockers, a 1295G head(ie Cooper S), an LCB header, and either an SU HS6 carb or a 45DCOE Weber. Hi-Lo suspension helps on the corners, and a beam rear axle instead of the rear subframe will make it dig in at the front even more whilst saving a lot of weight. All the parts are available off the shelf in the UK, but I don't know on your side of the pond.
The Mini-Marcos was a fibreglass monocoque 4"longer than the Mini,available to simply transfer all Mini parts directly into. It was more aerodynamic, a lighter , and of course the shell disdn't rust..One finished Le Mans in 1966. They are being remade now apparently.Mine was sold to Japan, after having attained a hilllclimb class record therein.