M1A "M14" in 6.5x47 Lapua

I talked about an AR-10 in 6.5x47 with my gunsmith, who specializes in building customized and accurized AR style rifles. He indicated that an AR-15 style would not have the magazine "length" for this round, and we'd have to go with an AR-10 to get that. he was all ready to tackle this, but I don't have sufficient funds to "pull the trigger" on the build, so it's on my wish list.
I think that is essentially what you are looking for, isn't it?
 
It is possible. One of the biggest problems you'll have is with port pressure, the wrong powder in an M1A or M14 can and does bad things to these rifles, the slow burn rate powder needed in the 260 or the 6.5CM (such as 4350) will deliver a higher than designed for gas port pressure, maybe an adjustable gas port, along with lighter moving parts/matched action springs etc could make it work.
 
Krieger would be your best bet for the barrel. 6.5 or 7mm shouldn't be a problem since it's just a matter of contouring a blank and they are already setup for it. Use the Shuster adjustable gas plug OR possibly a Sadlak national match cutout piston specifically designed for use with 168 and 175smk loads.
 
If you use a vented gas plug it should be doable as you need to use powder in the 4350 burn range to get good velocity. The old USN long range load in their M1 Garands was 54gr IMR-4350 with 190's and they did this will drilled out gas plugs. I have seen others with M1A's in other cartridges. However I would go .260 Rem as you will have a wider variety of brass to choose from as using LC .308 will probably be your best option so it lasts longer.