Yet another wheel Q please

[Jerry 92RR]

I looked for a beating a dead horse smiley... there isn't one.

I found a set of 996 two piece rims I really like for the 97 Box. I searched the forum and found someone running 21mm spacers to acommodate
rears: 18X10's ET 65 with Pirelli 265 35 ZR 18's
fronts: 18X7.5's ET 50 with Pirelli 225 40 ZR 18's
for the rears. I was hoping for confirmation on this as well as my assumption that spacers are not needed for the fronts.

I believe they are similar to these: http://www.theautobahn.com/forum/showthread.php?t=17779

Also, another embarrassing question: how do the spacers work? Do they come loaded with new bolts and I use the supplied nuts for my old lug bolts to hold the spacers on?
TIA