For it to bog that bad I'm thinking carb but with 2 carbs acting the same I'm thinking vac leak. Total normally should be 35 on a SB (checked with vac adv capped) but with mags then 31-32 is a good ballpark & that get set AFTER the initial is set (vac gauge method works good for initial) but all that needs to wait till the problem at hand is solved. On a side note what is the idle speed in drive & the advance starting at 1600 is a bit late but that's not what's causing it to bog that severely. the compression test tells me the long block is healthy & that only leaves ign or vac leak (intake/PCV). I ain't a cam guy so no opinion on the TC but that is a SEVERE bog