Get a new battery.
Ethanol is horrible for storage. The alcohol absorbs water.
Pull your supply line at your accumulator and hook up a hose to a container, run your fuel pump with the jumper method to empty your tank, and get rid of it in your lawnmower after adding some octane boost.
Add new gas, run it through the system until you see nice clean flow out of all 6 injectors.
During your testing have you checked the vacuum booster line to see if it holds vacuum? Could be the massive leak you are looking for.
I left a hose off of my AAR (Big yellow/gold disc thing) in the back of the CIS that I couldn't see. The rubber y-pipe back there has been known to crack, have you put a mirror back there to inspect the rear hoses and connections?
Like this post shows.
1976 911S – from garage find to on the road