b-series conversion is possible. easiest way to do that is through hasport gear. you need to source hasport mounts, axles and wiring harness, jdmyard seem to be able to get that gear.

d-series sohc vtec is possible, but most people tend to steer me away from that. personally i wouldn't mind a d-series turbo vtec, that would have some balls on it...

they are your only realistic options, unless you have a heaps of money to spend.. then you can do pretty much watever you like