273 Engine will not start - Ideas?

Agree. Checking spark. I like to get "right to the coil" so to say. Use some sort of actual wire to temp. replace the coil secondary wire. Rig that to some sort of test gap. Crank the thing, and if you can, use a wide test gap, 3/8 to 1/2" The thing should make nice hot blue snappy spark, and if you crank it 2-3 seconds or more, should make nice rhythmic sound. And Crackedback pointed out on here, which I previously just never thought to suggest, is that you can check timing "on the starter"