Hello Mayhem!
The piece you are talking about is also called "Part 91", and it is officially what Tanaka users call the "virginity piece". It means that your rifle becomes a man when Part 91 breaks..which will happen after a while eheh
You buy your Tanaka stock, have fun with it for a week, BANG, the piece breaks and then you are out to buy a replacement.
Material wise, all upgrade parts for this Part 91 from G&G, Creation, Best gun etc. are good because they are not plastic.
Problem is, they are somehow out of spec and most miss the second pin that you use to secure the piece in place.
To counter this, I did the following:
http://www.airsoftsniperforum.com/showthread.php?t=2526
Feel free to let me know if you came up with something similar, equal or different.
I have a lot of upgrades on my M40A1 that sound exactly where you are heading to..Laylax 6.03mm 403mm, KA conversion, etc. etc. and I am soon going to enter a long range target shooting competition with this rifle, I think I'll film it with my go pro, from the day I start upgrading and taking care of my rifle (been in the closet for almost 9 months) to the day I start the contest.