How much trouble, time and expense would it be to convert a nice set of '68 buckets to '70 standards?
Would I be better off looking for a descent set of '70's?
Thanks in advance for your help.

I think it would be cheaper to sell the 68s and buy a set of 70s. If not you would need to purchase a set of backs/back covers and headrests. Actually you could use 69-72 A body buckets as they are identical. 68s are very similar except they have the back release on the side and most don't have headrests as they were optional in 68.