Re: M1a 260 build
I've been thinking about this for many years, using a free-floated design for the M14 gas system. The challenge is with the tappet short-stroke gas block, op-rod guide, and how the M14 action mounts to the stock.
I have a design that I shared with Sage, but they haven't pursued it to my knowledge.
You need a dual-pillar bedded, rear-lug receiver for starters if you want the most accuracy potential. You have to isolate the Achilles heel of the M14 from the barrel, namely the cylinder with floating tappet.
Once you find a way to do that, and have a trued-up bolt and receiver, with a high-end barrel, securely mounted in way that is repeatable, you will have a competitive gun again against the AR platform, but it will take more work, just not all the witch's brew concoctions gifted armorers have had to learn over the past 6 decades to make that gun shoot when the correct star alignments are in-place.
You will also need a sturdier barrel profile for the forend.