This may be a radical idea, but if you're going to have your hands full anyway, how about:
Disengage the autopilot
HAND fly the turn
Reengage the AP on the new heading.
Yes, in general that's about the only way to make a stable turn with the coding of the Sperry A/P on this model. The only retired Pilot I knew (who's long since been deceased) who flew the old C-69 and later C-121 told me they rarely to never used the A/P during maneuvering, climbs and descents, all hand flying unless they were flying straight and level, then they'd use the pitch hold to reduce the workload. I have heard and read the same thing from a number of other Connie Pilots over the years.
Anyhow, as I mentioned before, the one issue with the Sperry A/P coding that makes it nearly unusable for me is the fact I cannot get it to hold altitude, it's either a hair too much up or down regardless of fine tuning the trim. The issue is simply that the adjustments are still too coarse. If that issue could be fixed, I'd use the Sperry 100% of the time and hand fly the turns, ascents, and descents and not even fool with it for maneuvering.
As far as the 2D FS autopilot, even with low weight (moderate fuel and passenger/cargo weights), at target airspeeds and a 500fpm climb (yes, in stepped climbs if necessary), I am still encountering the porpoising (mild pitch oscillations) if flying above Fl 180. Oddly this issue does not occur when using the Sperry A/P. Bottom line, there's a bug or two here, not a weight and balance issue nor me attempting to fly the model out of performance parameters thus inducing the mild pitch oscillations during level-off over FL180. I am a Licensed Pilot and have been since 1990 and I know full well about performance & weight and balance limitations of any aircraft I've trained on to fly.