Ishi,
I find that rounder bodies tend to roll more.
I make my swimbaits with flat, tapered sides. They are tall and thin. I make them from 1"+- PVC decking.
They generally start out 7/8" thick at the back, and then about a third of the way down, I start my taper, so the belly is 5/8". This still leaves plenty of room for ballast and hardware, but I find the flatter sides reduces roll, and the V cross section lets me burn them without roll at high speeds.
You bait looks almost round, so it has a lot of buoyancy to overcome to get it to sink. If you flatten and taper the sides, you will remove some of it's buoyancy, and should be able to remove the ballast in the rear section, or at least reduce the amount of ballast you need to get it to sink.
I hope this helps.