Thanks. More questions (sorry I'm such a pain):

- Would it be helpful to move everything out of the room above it
before we start banging away, to reduce the weight on the joists from
above?

- Is any jacking needed to get the weight off the joist before banging
on it or will the banging be enough?

- Does the blocking have to be right over the central beam or can it be
off to the side a little? I ask this because of the stupid plywood
gusset. Because it doesn't cover the full width of the joist I don't
think I could get smooth fit - there will always be a gap between the
blocking and the joist at the un-gusset areas above and below the
plywood.

Here it is viewed from the side:

______________________________________
joist 1 | joist 2
___________________
| |
| gusset |
----------------------------------
|
---------------------------------------------------------

- And since there is no joist overlap at the beam should I be running a
line of alternating blocking down either side of the beam, since the
joists aren't really joined well and when I block one joist it won't
100% stabilize the other side?

Aggression and exhaustion won't be a problem, I'll just pretend it's
the building inspector :lol: .
..
Everything you explained was "state of the art" for the 1970's.

That's a terrifying thought.

They don't build em like they used to, and that's a good thing.

You got that right.

Liz