There is no chance that the ICs will fit in the tek, or any other fixture I have seen. I dont know the true dimentions of the ICs, but I can guess that the 660 is about 10"L x 4"W x 2.5"H. New ICs also include the harness, which should be all teh wire you need to hook them up externally as well, assuming you are remoting them at a great distance.
Externally is the way to go, and would actually benefit the ballast by keeping it cooler and giving more space in the fixture for fans/cooing devices. It should be easy enough to do. The only thing else to consider is that the lamps will really need a good cooling system, so get ready to cut some holes for fans in the tek. I think it would be neat and worthwhile, though.