I have a 10 bolt (68 Chevelle) and will be installing a 12 bolt (70 chevelle) will I need a combo u-joint and if I do can anyone recommend one. If they are the same on both ends can anyone recommend a type to use for replacing both.
thanks

pretty sure that the u-joint you have in there is the same
not sure about this though but I think you might need a shorter drive shaft
if you can get the drive shaft when you get the rear you may want to get both
again not completely sure here but I have run into problems where the drive shaft is to long after drive train swaps
never checked if it was the rear or the trans that makes the differance
someone else may be able to clear this up but I would try to get the driveshaft also

I have done the swap from 10s to 12s with no changes needed with the shaft or ujoint.

yep, swapped out 10 for a 12 bolt, everything bolted up, ujoints included.