Checking cam timing on assembled engine

Is it possible to check the cam timing on an assembled engine? I have low vacuum of 8"-9" at ~15* advanced initial timing with distributor vacuum advance and brake booster both unplugged and capped. I've had it apart twice this year to replace the timing chain and the intake manifold gasket. Neither helped with the low vacuum issues or changed how the engine ran.

'69 340, Edelbrock performer intake, Holley 4bbl carb (600 or 650 can't remember) with spacer, unknown cam