Only things I can think of are:
Undercocking kit (Mike has many left in stock in black and smoke color)
right feed stock class body
but that's all redundant and will just leave you with extra parts
center-feed open class body
200 round hopper
3.5 oz tank
Rear gauge would be nifty but you'd be buying another valve? Unless you make a hole for it to fit?
Or you can skip all that and get the gun Aurora plated if you're going to get a lot of money! But you'd have to find out where, if they still do that.