Taking the front carb first. The nipple for the Vacuum Retard on the distributor is on the bottom of the carb. The hose runs to one of the 2 fuel traps up by the thermostat/ water pump housing. From there to the Thermostayic Vacuum Switch (TVS) on the top radiator hose; from there a single hose to the distributor's Vacuum Retard.
Still on the front carb. From the nipple on top of the Throttle Bypass Valve (TBV)housing to the other fuel trap near the T-stat. From there to the TVS.
Now the rear carb. From the TBV to a "T" joining it to the front carb's TBV hose.
Still on the rear. Fron a nipple on top to a fuel trap to a "Y". Also to a leg or arm of the "Y" a tube from a vacuum breaker switch activated by the carb's idle speed cam.
That leaves 1 leg of the "Y" that leg holds a tube to the top of the EGR valve which is mounted on the cylinder head.
The 74 was unique in it's emission plumbing and in my view the most complicated, most of which can be eliminated or disabled.
Here's a picture of my 74, stipped down as much as I saw fit.