ah ok bummer, i guess you have to cherish the days when your licence is clean and youve had no accidents. 600 dollars full comprehensive is damn good then considering.
well in that case with a stock E88 and standard head gasket your looking at 12.9 to 1 compression, even higher with the E31. with a 2mm head gasket its a more reasonable 11.7 to 1 but still thats very very high. check out www.zcarclub.com.au go to the technical section and download the engine builder by walter fath. really useful stuff.
i had a very similar problem a couple of months ago. a vibration occured above 45 miles an hour only when accelerating, at first i thought it was the fly wheel coming loose:( but it turns out that the tailshaft was coming out of balance. after a couple of quarter mile runs at the local strip it was so bad i had to tip toe home. one balance job and two new universal joints later (even though they looked OK) and the car is the smoothest its ever been. hope this helps
boring the l24 block to 86mm shouldnt be a problem, but Ed is right, the l28 block is already at 86mm, and you can bore them to 89mm, fit KA24 pistons and a standard l28 crank and get 2949cc.