HEI Firing order

[ratman90]

My BIL gave me a 72 C10. Looks like someone got 90% done and gave up.

Spark plug wires were atrocious on this engine, I assume 350. Held together by zip ties. And way too long.

Bought a set for a 75 better and they looked to be ok. Now is the weird part.

PO had #1 plug wire In the back at what every other picture calls # 5.
ACCEL HEI Super coil 140003 coil? Ran fine. Just wanted to put correct length wires and rout them nice with some separators. Kind of hard to do. Ram horn manifolds and AC compressor in my way.
So I routes them per the normal diagram that is all over the net with cyl 1 on the cap facing cyl plug. And 6&5 running parallel with the firewall.
18436572 with 7 being on the firewall side of electrical connections and 2 being on radiator side of connections.

Problem is it will not start but backfires through the tailpipe.

Did not turn dist or mess with timing.

Removed accel coil and replaced with parts store coil and dust cover. Still backfires.

I thought # 1 could be anywhere on the dizzy as long as you followed proper firing order? I have double checked. Double checked with my son. And then had him double check. Wires are routed correctly.

Thoughts?

Larry