I used shoebox's site http://shbox.com/ci/fastener_matrix.html to find the specs on these 3 bolts. If I am looking at the right one on that page it states:
Optispark Mounting Bolt 106 lb. in. 3/8" 1/4"-20 x 2.75". I bought some grade 8 bolts in this size but they sit almost an inch too far out.

This is on a new lt1 383 shortblock. Initially, I tried to place the bolt in but there was too much rubberized rtv. I stuck a screwdriver in the holes to remove it and was then able to screw the bolts in. But all 3 bolts seem to stop nearly an inch away from where they should I can get plenty of thread or turns on the bolt. I'm figuring on just getting shorter bolts, but want to be certain that I'm not bottoming the bolts out on something else besides the block itself.

 

just get shorter bolts, 1.75 or 1.5 long ones

 

That's the length my reference source say the bolts are. I guess there could be an error. Let me go pull an opti bolt and get back to you.

p.s. It may be a while.

 

2.75" is way too long. I agree with Dave that they're somewhere around 1.5"-1.75" long.