Help finding heater core that fits '66 deluxe heater (w/ AC)

[Rust-O-Matic]

I recently tore down, stripped, fixed, and repainted all of the original heater core housing parts on my 66 C20. I picked up a new core from Classic Parts because my old one was seeping. I opted for the more expensive copper one over the cheaper aluminum version, because the core dimensions of the aluminum one were not the same as my original. The copper one was basically identical to mine though.

Tried to put it all back together today, and the heater hose necks sticking out of the core are not in the right places, and therefore will not fit. It was not off real far, so I tried to bend them slightly, and you guys know what happened... the solder joint popped and the tube fell off in my hands.

I'm gonna take it back to Classic next week and see if they will take pity on me and swap/refund/something. I'm trying to get this done in time to go to a local car show next weekend. So my question is, if Classic can't help me find one that fits correctly (I'll bring the housing with me when I go), can any of you guys recommend a brand or seller that you know for certain fits? Once again, just to be clear, my setup is the Deluxe heater that uses a little larger core than the thrift setup.