the brand of your car is very important as it might need a long shaft or short shaft to fit your gearbox and clutch,also you need an engine with the exaust port on the side that will fit your car. i dont see why you dont want the cooling head..are you sure the one you have will fit the new engine? anyway it wont cost you more as it comes standard with the engine.
anyways look into o.s. engines .18 size ,bigger than that will not fit without heavy moddification of your car
just pm me with 1 or 2 pictures of your car and i could try to find something that might do the job pretty good