I had a similar problem with one set of forks two bolts sheared and the others were real tight,
The sheared bolts i drilled out and fitted stainless steel inserts (helicoils)
the tight ones i warmed up the triple clamps (i used oxy acetlene) but you need to be very carefull else you will end up with a pile of molten ali on the floor, The other option is to put the clamps in an oven to heat up then attempt to undo the bolts.
