Probably not the way you want your question answered, but the broken bolt has the same thread pitch as the other three that (presumably) aren't broken. Just take one of the others down to your local mom and pop hardware store where you buy your taps and see which hole the bolt threads into on the thread identifier board in the nuts and bolts aisle.
I think you'll find that p/n 255207 is 1/4 UNF x 3/4 bolt, but verify that at the hardware store. The 8.8 suggests that it's the equivalent of about a grade 5 bolt.
--Mark
1973 SIII 109 RHD 2.5NA Diesel
0-54mph in just under 11.5 minutes
(9.7 minutes now that she's a 3-door).