Just spitballing here. No experience with a 6800.
I can’t see the blowdown being a big problem at 25 degrees but you would probably get a larger bump in performance if you raise the transfers as well.
75/101/126 will probably run pretty close to stock with a tiny bit more grunt. How much you widen the exhaust will have additional gains. If you can widen exhaust to 65% of bore you may see enough rpm to warrant raising the intake a little farther. Raising the transfers to 123-4 would probably get you there as well.
There may be simple flow gains in other areas that are worth finding. Often air horns are restrictive, transfer lowers and tunnels have obstructions or rough surfaces, mufflers don’t match exhaust etc. I think that stuff is really important for a BG delete port job.
I have a feeling it will be a ripper, just because it’s an old Dolmar.