lutfy: I got one top crash bolt break on me, but it could be due too late noticed wheel bolts slightly undone after wheel change yet still keeping tracking, not re-tightening them as i should.
As for slipping .. people sometimes use paint to prevent such. It extra glues/holds bolts in place, and is often used with something that may slip much more, eg. if you slot your struts for more camber. It's hack, but it works
"two SPC bolts on both ends" .. camberbolts are already smaller in diameter then stock to allow play for adjustment. Use proper 16mm camberbolt on top hole, and 14mm camberbolt in lower hole. I wouldn't risk using 14mm camberbolts at both.
With whiteline's KCA416 16mm camberbolt top & SPC 81305 14mm camberbolt bottom, at stock hight i got -2.2. Not exactly your aimed -2.5, but imho a bit safer then SPC 81305 at both holes.
P.S.
To lessen understeer on track (and get better more even tire wear) of course right way would be to add neg. camber on end that needs more grip, front that is. But as there is limit how much camberbolts can help, there is option of removing grip on other end too, to get wished grip bias. As many advised, i'm running by 0.5deg camber less (-1.7) in rear and find that doing exactly that, changing grip balance more to my liking with stock.
In ideal world there would be also whiteline's com-c offset rubber top mounts to go along camberbolts for extra camber, but unfortunately they didn't manage to fix bearing failures thus delisted twins as compatible with those. So if you need camber more then what is provided by camberbolts in both holes, there are only two options - slotting struts or camberplates (unfortunately in absence of com-c only pillowball ones). Also, if you lower your car, it will naturaly gain negative camber too. -2.5 camber should be easy to get with camberbolts in both holes for cars with lowering springs.