Won't start - obvious things to check?

[ssuesens]

Phone just rang. Son is stranded 3 blocks from the house - his 71 C10 died at a stop light. I just towed him home and will go look at it tomorrow morning.

Here is what I know. The motor has always been VERY dependable - it is his daily driver. Last Sunday we replaced soft fuel line for a hard fuel line from fuel pump to fuel filter before carb It has been working fine until tonight. Tonight we checked fuel filter and it had gas in it. Checked carb and it had plenty of fuel as well. Cranking sounded normal - just didn't start.

I know from experience it is usually the last thing you messed with but it appears it is getting plenty of fuel.

So I ask the better mechanics than me on this board (almost all of you) what you would look at first.

Additional info:
350 AT
HEI Dist (Petronics flamethrower)
Holley 4 barrel