Put some ATF trans oil or spray penetrating oil on the seal, all the way around for 30m or let it sit over night is better. (Worst case-submerge the metering block into ATF overnight).
Then try putting two bowl bolts into (do not thread them) metering block and use that as leverage, if you need...
What was your highest manifold vacuum reading at idle, while in gear?
After reading what you’ve described, I’d start by checking the accelerator pump circuit first, to make sure it’s giving a good, immediate fuel squirt as soon as the throttle moves. If that’s working correctly, my next suspect...