That is going to make a nice set for sure. As long as you are fitting those 20 gauge barrels(which are gorgeous) I would have those 34" barrels fitted as well even though that might be more involved. I like the idea of 28 gauge tubes in those. Then you will have a nice 16/20/28 set
If you don't mind sharing, let us know who you are going to use to fit the barrels. Or send me a PM if you that's easier.
This is a great project. Not many 20 gauge hammer guns...