The Colony double nut lifters I tried to use had the base that was too small compared to the other lifters - single nut I believe. Vince Falter has a good section about repro lifters on his website - link below. He isn't impressed with the small base on Colony double nut lifters. I tried to adjust the double nut lifters and it was a real task as the part on the lifter base below the double nuts was below the lifter housing in the block. I suppose you could cut off the top of the lifter housing, but I don't want to hack up the block to fix a problem that shouldn't be happening.
Rusty Nelson
http://www.fordgarage.com/pages/valv...comparison.htm