Spending the extra money for a white feather isn't as ridiculous when you consider that a stock M1A will need significant upgrades to handle and fire reliably, accurately, and without cutting your eyebrow on the scope. I'd rather get it right the first time.
The rifles Armalite now markets as AR-10s, are not the same as the originals. None of them are. In 1995, former Army Ordnance officer Mark Westrom, owner of Eagle Arms, purchased the Armalite brand and the company became Armalite Inc. Shortly thereafter, Armalite introduced a modern version of the AR-10. The new Armalite AR-10 was patterned after the AR-15A2, scaled up to take the 7.62x51mm NATO (.308 Win) cartridge, along with various other design improvements intended to strengthen the rifle. Ironically, the original AR-15 itself was a scaled-down AR-10. The new AR-10 is offered in several versions including a carbine with collapsible stock, a target model, and one version chambered in 300 Remington SAUM. SIMILAR rifles does not mean the SAME rifle. Few if any of the parts are interchangeable, it is a completely different design.
The first thing I would tweak on a DPMS would be to put in a RRA 2-stage trigger. I would have backup folding sights with tritium inserts. I would switch out all the springs for Wolff, and I would probably shop for a better barrel and put a muzzle break on it. Is that alright with you?