I agree with 220, you have a mess on your hands.
I would do "whatever it takes" to get rid of the zinsco meter combo unit. You could:
Install the new indoor subpanel where you want it
Run a temporary feeder from your old zinsco meter / main (from a convientent double pole breaker in the zinsco for now to power up your new sub
Slowly move all of your old circuits to your subpanel, until you have no circuits old but the temp feeder to your subpanel. (and maybe the lines running though the plumbing pipe.)
Have the POCO cut off that meter panel and put in a new one. I recommend a 200 A meter main with feed through lugs, with a few spaces for outdoor circuits such as those that are running though the plumbing pipe or outdoor receptacle. Or, install a new meter socket and seperate disconnect, or just a meter / main. (and have the outdoor circuits tie into the indoor panel)
There is multiple ways to tackle this.