Just finished with mine. '74 with a 350/th350 and used Aldan coilovers. 11.75 extended length, used channel and moved the upper mount outboard 3/4" from the stock mount. Ended up trying several different springs and stayed with a set of 500# springs, cut 3/8" off the lower snubbers for more travel and it sits good and has way better ride than before.. Love it. Hope this helps..
PS - the reason I went with the heavier springs was the 350# springs were nearly at coil bind when I bounced the front end in the shop. Not enough resistance and I didn't want to break a spring on the street.
