Glad to see you stuck with it and worked through the issues and had some success! I am back after a rocketry hiatus and hope to fly mine again soon.
I did do some work on a larger RC version of the A4b. One of my flying buddies gave me an Estes Maxi Brute V-2 kit. Some research showed that different releases of the kit has some pretty significant weight differences in the blow molded nose cone and tail cone, with the earlier releases appearing to have the lightest parts.
I think you could do a successful BT-101 size A4b using the early lighter parts, with dump-able water ballast nose weight to get rid of the boost pod. This could do well on various 24mm reloads.
The ultimate version might be to splash the nose cone, tail cone and the vac formed fins of the Maxi Brute V-2 and do very lightweight glass parts for the BT-101 tubing. This has the potential to fly at a nice light weight. Downside is amount of work involved and a rather fragile nose cone.
Might be able to have a thin wall ABS 3D printed nose cone and tail cone created that would be lighter than the lightest Maxi Brute kit parts, if a little heavier than the lightweight composite parts.
So many project ideas, so little time, even in retirement!