Erratic Timing

After you shorten the slots to say 22 degrees, and run an initial of say 12* for a total of 34*, then that long looper will no longer top out at the same Rpm as before.
I run one of those on my HO367; But In mine, it begins operation at 2800 and is done by 3400, and it only brings in 4*. This allows me to run a medium fast curve to 2800 for sharp throttle response yet by slowing it down after 2800, I can run 87E10 @185psi cylinder pressure with aluminum heads, at full timing, without detonation. So, that little tiny spring has , over 125,000 miles, saved me untold thousands of dollars in not having to run better fuel.
BTW 2800 for me is 20mph in first,33mph in second,45 in third, and 64 in fourth...... so in normal driving, I never miss those missing 4 degrees. And at hiway speed in 4th the timing is locked to 28*. To that, my Vcan adds 22* for a cruise total of 50*, very conservative.
I think I stretched that long looper just a hair. That was over 15 years ago so please forgive me if I cannot recall. You have to be real careful cuz there's no going back; once it's too long it is no good to you.