you could always buy a 240sx and then strip it down to the weight of a civic?
thinking mounting the engine in the bay, not that hard, engine wounts are easy to fab assuming you have a machine shop.
there is an exhaust tunnel, with some creative shift linkage (maybe the 240's are cable which would be easy to manuver around) that would mean minimal cutting for the driveshaft.
rear suspension? you would have to integrat ethe nissans and the hondas. Keeping geomtery uniform and in the realm of what you need to be drivable and safe would be very difficult.
front suspension would need to be sealed some how since there are no axles up there to prevent water from getting in to the bearings, unless you want four wheel drive then that presents a whole new set of problems to get around. like finding a nissan fwd system that would actually fit in a civic without need to bulge everything out.