I think it would be easier and cheaper to find one in a breakers over in the states mate. It'd cost a small fortune to send it across due to the weight
It possibly is because the exhaust is off. The cams might make it a little lumpy but I wouldn't imagine it's would make it sound like it's missing tho. Well done anyway. There'll always be little niggly problems with things like these but you'll sort them I'm sure
The slight miss could be plug leads mate. When it's dusk have a look down each plug hole while the car is running and you might see the leads arching out against the head that's what was wrong with mine so it was a nice easy cheap fix.