Closed Vent to Open Vent Fuel System

[jedab72C10]

Greetings all, great board, been reading for about a week and would like to ask some advice. We inherited Dads 72 Chevy pickup C10, 350, AT. He was about 95% complete on a total restoration when he passed away. We'd like to finish it but I am undecided on one particular thing.
This model has the tank behind the seat. Its a small tank so Dad added a saddle tank on each side. Now there is a 15 gal on each side along with the 8 gal behind the seat. There is a switch that you turn to determine which tank to choose. There is one problem with this that was not thought out or finished. This model uses a closed fuel system. If you use the middle tank its fine. The problem is when you use one of the saddle tanks. The return builds so much pressure into the tank behind the seat, it could literally explode if you don't switch back to it or use it to relieve that pressure from the return. It would be difficult for me to put a return to whichever side tank I was using to keep the system a closed system. So I think I should open it, use a vented cap, and cap the returns to the tank behind the seat. What can I do about the fuel pump ? New one ? or cap the return for that ? If you have any other suggestions for this they would be appreciated. It would be really nice to eliminate that gas smell in the cab too, I am replacing some hoses and the fuel sending unit which didn't work, to get the gas guage back too. I don't have senders for the saddle tanks. Does anyone have a slick way to determine fuel levels in the saddle tanks ? Thanks in advance for all of your input.