How do you know if your 1967 350 is on compression stoke for piston 1?

You will need a another person to help you do this.
Remove #1 spark plug and get someone to bump the engine over alittle at a time while you hold your finger over the #1 plug hole and as soon as you fill it blowing out compression from under your finger and it stops, Then #1 piston will be at TDC. TOP DEAD CENTER. You may have to bump the engine over a few times to get the feel of it.
When #1 is at TDC then the timing mark on the harmonic balancer will be lined up with zero on the timing tab on cover.