HA HA! Thanks a lot. Yes, I had a little rust forming this morning from drool at the local indoor range. I love bringing belt fed stuff in there, just for the reaction and , "WOW, is that legal??"
I am using an m60 spring and doing exactly what you said as far as cutting and adjusting. I think my main problem is a loose/leaking gas system. I'll try again today.
As for fun, entertainment, it has been the best project I have done to date. A SOLID 13+. I have really enjoyed it. As for challenging, you cna't be timid, just make the decision and go for it. Just cut on the cheap parts first. I am very much a hack,tinkerer. I did it pretty much, "cut close, beat to fit,paint (weld) to match". I would lie awake many nights waiting to get up and go play with it in the garage.
I am already thinking of doing another, but it would really be based on the links and TC I could find. I have another brand new RPK just waiting.