I have a Proto SLG UL 09 and the only thing that changed was the barrel, moved to a dye UL, and an on / off cp. some people also change the feedneck, but I found that there was no longer needed.
Moreover, as stock comes from this very well.
I had a problem with my Proto SLG board a couple months ago. Apparently there was a glitch when they made them so call up Dye and they'll send you a new one for free. All I upgraded on mine was the barrel to a Dye UL and an on/off ASA.
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Get the gun and USE it before you add stuff to it dude. The only things I suggest, What kind of SLG is it? Get an on off as to not ruin your tank.
a clamping feedneck to protect your hopper. Other than that, nothing is really NEEDED unless you see fit.