First thanks for helping me! I’m replacing my timing cover on my 70 350 gs ....before pulling the distributor I rotated engine by hand till rotor was pointing towards cylinder 1 on cap and harmonic balancer mark was on 0. I then removed timing cover expecting to see the dots lining up on the timing gears but the crank was at about 12 and the cam about 12 .....am I on tdc on exhaust stroke?
Next time remove the number one plug and stick a wine cork in there. Then you will know when it pops that you are on the compression stroke.
I would still confirm TDC on number one by using the cork. Unless you don’t plan to take the timing set apart (or rotate the engine) in which case you can simply re instal the distributor as it came out, ensuring the rotor points the same way.
Incase it gets over looked, be sure to properly set oil pump gear end clearance to .002 AND pack it with Vaseline to ensue the pump primes.
If the engine was running at the time, and you lined up the firing end of the rotor with the #1 tower of the cap, then you are on the compression stroke. Valve timing and ignition timing are two different things.
Any GM that I worked on, both timing marks at 12 and 12 was on cylinder 1 compression. Both marks together means it's on cylinder 1's running mate, which on an 8 cylinder, is cylinder 6.