I've never had a problem with Kirban but it appears that the same can be had from this other vender. Looks l to be the same product. Might be able to get it cheaper but this was a quick search. You do want the 2 core with the large tubes if you go aluminum. But if you stay with the copper core the four core will cool better. Just differences in the way the materials conduct heat. If you can find a two core aluminum with 1.25" tubes it is even better than the 1" tubes but not sure anyone makes one like that with the trans and engine oil coolers.
Keep looking. Ask around on sites like Yellow Bullet or the H.A.M.B about a reputable old school radiator shop in your area. I'm sure there is at least ONE. Where are you? Maybe someone here knows of one.