Have an 02 mcs and I got 15mm spacers for the front. They are hub centric and name brand well I found the stock to be 28mm from a site so I figured I'd need 43mm I could not find 43 and got 45 since they went from 42 to 43. Well my damn 45 are too long. Probably a 1/8" too long
Can I grind off the bottom of the bolts or will that not be safe for daily and autocrossing?

 

I am not sure what grade they are made from, but usually cutting a bolt does not affect its integrity as long as you do not cut it too short. ( i only mention grade of metal in reference to heat temper and hardness. you may just need to be careful of the cutting method you use)

The main problem comes that when you cut a bolt it tends to be at a slight angle as well as flat bottom, so starting to thread the bolt becomes quite difficult. As well as you will need a die or a thread chaser to make sure all of the thread are fine after cutting. (cheap way is to thread a nut all the way onto the bolt before cutting, cut, then take the nut off. It should straighten threads as it comes off)

I am sure there are correct length bolts out there.

but if 45mm was 1/8th to long, that would suggest you need a 42-41mm bolt. 9.125"*25.4=3.175 mm )

Personally I would either just find the bolts, or contact a bolt/stud manufacturer and have them make me a set.

 

cutting the bolts is doable, but it can be a huge pita.

also, anything over 10mm, really should be an adapter. normally at that width they convert it so you can bolt it to the hub and then use either the new provided studs, or your old bolts to secure the wheel.

a 15mm spacer is pushing your limits on the bolt length, in my opinion. i have 8mm spacers on all 4, and just used slightly longer bolts.

a good judgement is to watch at you tighten. mark the bolt on the head. if you can get at least 6 full turns before the bolt bottoms out, generally that indicates it will be safe enough to drive on.

and whatever you do TORQUE the bolts at least to spec. i believe that to be somewhere around 65 ft/lbs. i torque mine to 90 ft/lbs just to be safe. theyve never loosened up on me and ive never had a problem getting them off.