/6 Timing has me stumped!

Looking for some guidance or suggestions.
Newly rebuilt '68 block slant six. Timing gear lines up correctly. Set motor to TDC and point rotor to #1. Motor won't run. Fiddled and worked distributor around until it fired. Engine is running 120° out. If I hook timing light up to the #5 plug, timing is pretty much right there. Not running real smooth and is showing signs of vacuum leak. If I hold hand over carb, rpms climb maybe 200-300 before i can choke it out. Haven't had it on the ground yet to see what it does on under load, like maybe fall on its face? any positive help is appreciated.

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But "THAT" seems to be off a full tooth. You need to address that "FIRST".