Drilling new holes will probably be very very tough anyway, the metal which it bolts to is going to be VERY VERY VERY strong. We found this when smashing up a stripped bare crashed S13 shell for a laugh. lol Plus it would probably weaken the area considerably.
Rather than drill new holes I think ovaling the holes is a better idea like Steve suggested, I don't think I'd want to do it and you'd have to do the bolts really bloody tight to stop it from slipping back, and the studs on the topmount aren't designed to be that tight.