72 360 first start question

massive vac leak. & set the timing marks at 15BTDC. turn dist housing slightly till the magnet is dead even with the tooth. (the rotor will be at either #1 or #6). find the leak first tho, intake gasket shifted/mismatch/open (uncapped) nipple/bad carb base gasket/leaking vac line/hose. EDIT one tooth off on the t chain will shift phasing 15.6 deg on the crank, not sure it'd even run like that unless the chain set/cam was mismarked which it does happen. You might get rockover on #1 or #6 & see if the dampener slit is within a degree or two of TDC. pull the plugs for easy turning. get the slit on TDC & using a 1&1/4" socket/breaker bar move the crank back & forth a bit from TDC & note which (#1 or #6) pushrods both are moving, the cyl that they are moving then move the crank back & forth & hit the spot where both pushrods are moving and are at the SAME height & at that point (rockover) the TDC slit should be within that 1 deg (2 maybe) of TDC & this is with a tight/no slop chain. if so your phasing is OK & the prob is elsewhere & you dont have to open up the t cover & mess with the chain. keep us updated on how it goes. MORE EDIT for dist phasing, with the slit at 15 BTDC and the magnet dead even with the tooth, the rotor should be pointing (with springs retracted which they should be at rest) somewhat close to the cap terminal and the can will shift it CCW (on a SB) from that at rest position when it starts and you are above ported. SHORT VERSION: Confirm cam and dist phasing (dist phasing first cuz its easier) & if one of them ain't it then start searching for a vac leak