What's my options, I need to replace the radiator, it's done.
I still have the 273 in the car but the 340 is waiting in the wings.

What should I do to get back on the road?

recore my stock one?

go big money aluminum? (will it work with the 340)

Is there another option with a different stock radiator?

I used a stock 3 core radiator out of a Jeep Cherokee (round headlights) wall to wall radiator between the supports and I just had to braze on tabs to secure it to the frame rail. in and outs were the same size and I think I even used the same lower hose. Good enough for a 451.

Anyone else?

When my brother put a 440 in his 64 Dart, he used a later rad from some mid 70s junk (Cordoba?). It was the right height, but quite a bit wider, he had to trim the inner flanges of the front rails to make it fit. It had 2 rows of wide tubes. That car would not overheat. We had a nice piece of road in front of our house where we did back to back 1/4 mile passes for about 20 minutes. The gauge never went above 180 I don't know if you want to modify your car any, but I thought I'd throw it out there.
Travis..

I had the small block radiator for my '65 Coronet recored and the lower tube moved slightly to the left for a big block. Before I had a chance to install it, I ended up with the proper 426 radiator for the Coronet. Long story/short, the radiator fit my small block '65 Dart like a glove. I used it for 3 months before going aluminum for the weight advantage (race only). Having said all of that, maybe you can find an early "B" body radiator easier than an "A" body one.