Not trying to be unkind but this is no beater guitar and if you don't know what finish "blush" you might want to consult with someone who does.
It's pretty impossible to help from here in that I would need to see it in person to better understand where you are with the reset.
The fretboard extension should be loose from working the pallet knives carefully and being mindful of runout.... You also have to know what runout is to be mindful of it.... We loosen extensions with heat lamps and shields AND bubbling finish is not allowed... The runout direction tells us the appropriate directions to work the pallet knives.
It's true that some L-OOs did have the top installed over the dovetail pocket after... the neck was installed and set. Not only was this an incredibly stupid thing for G*bson to have done it makes resetting much more complicated..... Some of the other lines that G*bson made in this time period such as Kalamazoo KG-11's and others they did this same thing, install the top over the dovetail. It still can be reset though.
As Ken mentioned too you have to be sure that the steam probe is actually in the very small void behind the dovetail on these. The pocket is hard to hit.
G*bson was also known to use so much HHG that they often glued their cheeks to the sides..... No jokes please...
Anyway you may want to consult someone who's done this before on valuable, vintage instruments and who also knows how to cut the top away over the dovetail. We don't and won't accept shipped in work so not trying to get any business out of you, just trying to help you and the guitar.
Don't know if you understand that this is a highly coveted instrument, a personal all time favorite of mine so please, please be kind to this old girl she's important, rare, highly sought after and valuable? Thanks.