Will 318, 340 or 360 heads fit on a 273?

Having done the swap, I put 340/360 heads on "64" 273 .040 over. Not even close to a dog. I used "72" 340 "J" heads with 1.88 intake valves. Topped off with "71" 340 intake, TQ and the "72" 340 cam. The heads were milled .040 and .038 on the intake side to min cc, 64.7. I also had TRW forged 10.5:1 pistons and mocked up the heads to the block using offset dowels to center the chambers on the bore. I would not recommend doing that with your van though. Your "66" 273 heads flow about 10-15 cfm less than J heads throughout the range till .500 lift. 302's flow 10-18 less than your heads, and 318 heads flow in between the two with larger chambers. All 273 and 318 heads have the same valve sizes. So, I'd have your heads rebuilt, Get a nice 4 barrel intake, including a factory 340 and any 4 barrel carb, I find Carter/Edelbrock more reliable. Get a cable operated kickdown set up. Use a 340 throttle cable bracket. Put in an Isky E-4 solid lifter cam, or similar and enjoy. Use your exhaust manifolds and run duals or go the Commando route and go single with a 2.5 pipe from the Y with 2 glass pack mufflers in series.