I am going to add a 3mm spacer and inquired about getting Longer Studs. This is the response i got and wanted to know if it was correct...
If you're only going out 3mm, you may not need the longer bolts. That is, as long as you have enough threads making contact as you screw in the bolts. Per the H&R guide, you want a minimum of 6.5 turns for a 12x1.5 bolt. That equates to approx. 10 mm of load bearing shaft length.
As far as the longer bolts go, we just sell the H&R bolts. We don't stock the bolts, but rather order them and sell them with the spacers. Also, if you're looking for a nice looking polished bolt head, the H&R ones aren't shinny, but rather a natural color that would be best covered by some sort of hub cap if you are looking for show quality.