will 360 j heads fit on my 273

Bill,
Buy the 360 heads as a investment, not for the 273...Few things the 64-65 heads had the different bolt angles. The 292 cam is way too big. I had the 280/474 in my 273, sounded cool, but even less bottom end than before! I'd recommend cleaning up your stock heads, gasket match the ports intake/exhaust. Performer intake with a spacer or just the RPM. As far as the cam, I'd stay below 280 duration. I think comp makes a 268-270 solid that would work great with the high revving 273. That will easily spin 6500+.
I upgraded my Dart to a 360, mild rebuild, for what it would cost to do the 273.
Just my 2cts...
Bob