Help!!! won't start....Mechanic please!

OK just change rear main hooked all back up and nothing.... 340 engine. Ok heres what I know...
#1 Piston on top center ,distrib. pointing at #1 and Balancer on center mark....
Gas in Carb...
Everything else looks right... Didn't check spark yet but worked before dismantle...
1st: Am I looking at the timing right?? is it posible I have it 180 off? If so How do I know that??
2nd: How can I check spark...?
3rd: What am I missing?