So, the old flat back style 110 actions are solid. I have built several rifles off that action. The bolt and bolt head issue is a non event. Yes there is an indexing tab in the bolt body that can be removed or order a bolt head with the indexing tab cut out. Very simple solutions available. If you really want to get fancy just order a new bolt body. Also, keep in mind the firing pin on the old actions may be a large pin vs the small. Another easy solution is to buy the new firing pin assembly. They are cheap.
If the action is a stagger feed blind mag and you choose to update stocks to a dbm or magazine center feed style you will likely need to modify the action a little. This is just opening up the bottom of the action is all. Simple for a garage smith, have done many.
PRC on a long action works just fine, if that is what you want to do. A long action round such as the 6.5-284 or the 6.5-06 is pretty close in speed, maybe 100 fps slower. The 6.5-06Ai might worth the time but i'd prolly just stick with the 6.5-284, which I have.
I am running a 6.5 PRC on a short action bighorn and prefit proof 22" and my current 6.5-284 is on a 28' proof.