Outstanding! buy Now read all the Poly posts here. For the time being, shoot ONLY surplus NATO ammo (no commercial) until you understand all the headspace issues, which you will discover by SEARCHING thru all the posts here.
You don't need to go out and do any expensive bolt conversions or barrel swaps at this time.
So long as your COMPLETELY STRIPPED bolt will not close on a NATO Field Reject (also called NATO MAX) guage you will be OK with NATO ammo.
Get this:
http://www.brownells.com/.aspx/pid=41040/Product/7-62-NATO-MAXIMUM-CHAMBER-GAUGE
A standard .308 Field Reject will not necessarily be appropriate for now. But if the (completely stripped) bolt will not close on the .308 Field Reject gusge, then you are definitely OK for firing either NATO or commercial ammo.
You will need to get somebody familiar with the M14 (Not your average gunsmith) to measure the headspace, or thoroughly read the posts here.
The Polys were designed for NATO ammo so they headspace typically longer than commercial.
JWB