S2000....
Although a bike engine may have the ponies, it lacks on torque. They are not made to move the weight of a seven around and therefor need to be kept on the boil to have worthwhile performance and this will hamper reliability on the long run.
Another drawback is the sequential gearbox that will get tiring after awhile having to hit every gear changing down or up and cannot simply go from 5th to 2nd gear for example.
Lastly, reverse gear mods are always an issue
(read expensive and problematic) with bike engine installations.
You guys are lucky to get that gem of a motor with box, looms etc for only 2.5k. In my country its scarce as chicken teeth at a breakers yard and the other day one was for sale without any extras for the equivalent of 6.5k English pounds