You probably could have got away with a standard 5/16 sender without the return line from an earlier model and specifically looked for the 90 degree bent delivery pipe...Don't know who makes one without doing a search but since you've already got it I'd use it and mabe down the line when you swap another engine in it could use the return...
Just keep in mind that return will be submerged in fuel and needs to be capped off with fuel/heat in mind to avoid trouble....The exhaust is real close to the tank on the rear exit/slotted, tipped pipes...
A few thoughts on the venting issue...
Is the vent line functional at the connection of the tank/hardline union {above the tank} ???
Is it simply a matter of tube-cutting the cap off the canister end to make the run functional ??
If so I'd get a canister and hook the line up to it...
That would get the vent tube up above the tank as the factory intended...
Then either run the line to the carb as the factory did or just use the canister and leave the carb line off{venting into the atmosphere}...
And lastely,on the cheap, if the vent hardline is shot and not capable of venting to the front of the vehicle you could run a rubber hose off the tank vent but you'd need it up as high as possible under the car and use something like an axle vent to end the run...
Some have drilled a small hole in the pressure/vacuum caps to do the job but you run the risk of fuel spraying out when accelerating and I'm not sure how doing that would affect the 74 tank and vent system...{a 1 year,humped up wonder of a tank}