as jonny/others have said. if you buy a pump from toyota, its the whole assembly including rear housing.
you will still need to buy a thermostat cover ect. but this part is quite similar to 4ac. and also you can use ae82 4ac/4age/ae92 4age external thermostat housing cover, on the rwd rear water pump housing, and then you end up with a place for your thermo switch as well
thing is though. you can just use a 4ac rear housing, and thermostat cover. and simply attach your fwd pump to this, and use a fwd pulley.
this is the set up i have on my motor -
4ac rear housing. 4ac thermostat cover (slight difference in exit angle of pipe but it works) 4ac thermostat (but its the same fitment as 4age, including ae82/92, ep starlets, ect ect).
and whatever random fwd water pump i had lying around. the only catch is a cant use an engine fan. well youre not meant to. ive seen people do it though, and get away with it for quite some time. regardless i dont want to run an engine fan anyway, so its no problem.
also, not that its relevant to you niz, but the 4age bypass pipe and top water neck is compatible with this arrangement too.