Big bore w higher CR to compensate for lost low torque with a hot cam.
I think it is difficukt to keep the budget very low on a 40 years old engine. The bottom must be in need of new parts as chains, tensioner, bearings, oil seals, clutch.
Why not new rubbers inside the primary hub?
You must be an enthusiast that love these old CB's. You get a much better modern bike with plenty of horses for the same money it cost to restore and upgrade an old CB. I have understood in later years that I married my bike when I saw it for first time January 1979. I had to restore what I did to the poor bike in early 80's
Honda CBR1100XX Super Blackbird from 1997 -2005 in a good shape with good looking fairings for $3500-5000 US here in Sweden. Really much bang for the $. I would like to have one beside my CB750. Wife has to bless me and enjoy travel on holidays first....that can be tricky though...
My engine mods in my CB750 that will be in next season cost MUCH more than that! If I add all mods spended so far, double it....
Engine only...then add new tank, side covers, 4-4 exhaust, NOS seat, NOS fenders, new fork.......
I have a complete extra engine for left over parts...Just to assemble it when everything is on my shelves and floor in the garage. That is tuned too, 836, ported head w std valves, hot cam, Smoothebore carbs if used in another rolling chassie.