Recently built one for a customer. 6.5X284, Pendleton gunstock, Jewell trigger, Benchmark Sendero taper barrel in a 8 twist. Its a real shooter. I milled the reciever for the 700 trigger assy.
The 721 is the predecessor to the 700 long action. They were made from 1948 to 1962 (give or take a year or two). Had a few bolt issues if I remember correctly. I think with broken extractors but not sure. The fix is to just buy a new PTG bolt to fit and voila, you got an up to date action. Oh and drop in any new trigger too.
Aside from being an all around pretty gun action, I think a lot of the open sight target guy's like the striper cut in the top of the action for competition; much like the 40XB's have. At any rate it's a nice action to build on...
Just my .02