Are you getting ANY spark at the plugs? Take one out, hook the plug wire back up, hold the plug body against some bare metal and have someone try to start the engine. If spark is blueish, put the plug back in and look elsewhere. If it is yellow or non existent find out why.
Elsewhere:
Is there gas in the carb throat when you pump the gas? If yes, look somewhere else. If no gas, find out why.
Somewhere else:
Is the spark occurring at the right time? Check your timing even though you marked the distributor before pulling it out. Once timing is right, crank the engine to #1 TDC (which is also #6 TDC). Both intake and exhaust valves (have a little slop between the rocker and valve stem) should be closed at TDC of #1 when on the top of the compression stroke. If they are tight you are on #6 compression stroke, so turn the engine one more complete turn. Now remove the distributor cap and make sure the rotor is pointing at #1 plug wire.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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