Truck Repair: 5.7,1986 chev timming chain, back fire, lign

Question
On a 1986 chev 1ton 5.7 replace the heads and it would not start after it was done, check the timming and it seems to be right.Pull the timming cover and the dots line up,on both the 12o,clock and the #6 tdc pos.slack it is significant but we could not get it to start and it did a very big back fire.the Reason we had to put new heads is because it blew a gasket there are many miles on this work truck,but the ring grove is minimal.We are going ahead with a new timming chain and gears but I am afraid that I am missing someting I was hopping when I pulled the timming chain cover that it had jump but that does not look to be the case.any help will be appreciated.
thank you  

Answer
Hello Blas,
I don't exactly understand what you are saying the marks are.
They do NOT both lign up at the 12:00 position.(actually, they will, but that isn't where you want them).
The crankshaft gear mark should be straight up, but the camshaft mark should be straight down.
That is when you want both valves on cylinder #1 to be closed, and the distributor rotor to be pointing toward plug wire #1.
You may just need to pull your distributor and turn the rotor a half turn.

Van