I paid $800 CDN for the engine and trans, $150 CDN for the harness and ecu. Then, i realized that i didnt want the harness that came from the car, so i called up my local speed shop and ordered up a harness from painless performance(formerly painless wiring). it was $650 CDN. Now, for a complete engine and trans, your looking at about $1450 Canadain. If i were you, i would go for an engine out of a 89-92 mustang because before 89 the fuel injection was a the crapy speed density. 89-95 used the mass air sensor, but the engine in the 93-95 cars had weaker pistons. So, my suggestion is a 89-92 car.
Can i ask what your plans are for he engine? if you are going to tear it down and put performance parts in there, dont bother searching or worrying about an HO block. it wont make a difference if you are going to change all the components anyway. I dont even think they HO is any different..is it?