lets revisit timing
We see this scenario on the dyno sometimes. Locked or welded HEI or locked or welded Msd distributors are common in circle track racing. when you check timing with these setups you will notice starting from idle the timing retards as rpms go up. How much it retards varies a little but they all retard. What you can run into is that the timing the motor wants at the top of the rpm range ends up being more timing than what the motor wants on the bottom end of the rpm range. Example 36 degrees at 6000 rpm and 40 degrees at 3000 rpm. I'm not aware of a way around this while still keeping the simplicity of a welded or locked distributor.