I'm not posting this to bash springfield, I've been very clear throughout my history on cgn that I am not a fan but that is beside the point in this discussion but I'm stating it to be fair. I am biased LOL
BUT... while I have not worked on more than a couple or 3 dozen or so m1A's in the past few years , the trigger group was the number 1 reason the owner approached me to look at it. VERY VERY short hammer hooks , how they passed inspection I would never know.
word to the wise with ANY M14 type rifle that is new to you , learn about how the trigger functions and what to look for as an unsafe condition, if you are able to inspect it in person before a purchase..
I all honesty, I have serviced 9 , brand new SA trigger groups from rifles and at least a couple that where bought just as triggers.
here is what I found in just that small sampling.
unsafe trigger hooks
pin that holds the "sear" to trigger post not installed correctly (tight in sear and not trigger post, very wobbly sear)
cracked sear leg
all of the guys that brought me trigger issues chose to buy parts from marstar or treeline and have me rebuild the trigger over dealing with the hassle of warranty.
while I can't help you with the piston..... personally I would just replace the piston with a sadlak or GI
I can rebuild your trigger if you buy a garand or m14 trigger/sear and hammer....... I'll even do it for free if yer quick in getting it to me

after Christmas I won't be online much.