depending on how much work you are willing to put in, a 2.8 or 3.5 big six will (just) fit into the e21. i'm currently in the process of finishing a engine swap like this (euro 3.5 from a 635CSI into a 320/6). cornering probably will not be it's strongest point considering the added weight over the front wheels, but straight line performance should be pretty good with 218bhp on tap. want info? mail me at g.kleis@planet.nl