Those old Centerlines look mighty good to me. It's hard to believe how fast time goes by.
You may have more experience with nitrous than I do but a few thoughts. I have found it hard to pick up a precise amount with nitrous like you need to do. I have run 53 jets all the way up to 78 jets in plate systems- foggers and the difference is not as much as one would think. I have run engine off the line and then activated the nitrous in high gear, I have run nitrous off the line and then shut it off in high gear. Needless to say the gains are much greater when the nitrous is used off the line.
Looking back, a window switch for activation-shut off was probably the easiest to tune for a specific amount of et. Put in a rpm module for activation and another rpm module to shut it off. I always shut it off about 400 rpm before the shift so it wouldn't drive through the converter. I never did try a progressive controller so I cannot comment on how they would work in this situation. I ran Q8 dragsters and I had mine to come all in 400 rpm above my two step chip. I ran a fogger and it came in much smoother than the plates. With the plates sometimes the car stuck and sometimes it blew the tires off. Traction was much better with the fogger.
Just some thoughts, hopefully helpful, from previous experience. With different weather conditions you will have to find different tunes cause what works now will not work in the middle of August. Best of luck, I enjoy reading your posts. When I raced I had to do it all myself, like you. I had money for groceries or racing, my family put eating first.
One thing has been bothering me about the head work you had done. The car should not be slower or even the same. I hold RFD in the highest of regard, I think that is who did the work? I cannot figure out why you did not have a little gain at least. The only thing I can think of is valve job we did a few years ago. I changed a 45 degee seat to a 50 once and the car slowed down even though the flow bench showed gains. The 60 ft. was slowed and the lag at gear change was worse. We changed it back and the car came back to the old times. Your does not make any sense. Not being critical just trying to figure out why it didn't pick up even a small amount. Again, if this is not appropriate PM me and I will delete.