88-89-90 m3

I found a e30 M3 the year is 88 or 89 not completely sure but definately not a 1990. i asked about it and found that the problem it was just sitting for a few years is that the engine is blown but was not told what that entails. I was planing on offering the guy around 2 grand for it and rebuilding the engine. I really wanna hold out until i find a 1990 since the different engines and such. but this seems like it would be a fun long term project. with the results being an amazing bmw. just wondering on peoples thoughts about a 89 to a 90 M3 and if it would be worth it to rebuild the engine.

thanks