Have you cut and converted kegs before?.
No, I have not found the need to create any Frankencocks.
Kegs are barely worth the effort to cut the tops off to make a BK/HLT/MLT, much less try to weld two of them back together, or even worse, prep them to have to be sent out to get welded, just to increase the capacity by a few gallons. Who knows though, maybe this is the start of a movement and someone will start making commercial 2 BBL brewhouses using stacked 1/2 BBLs. But why stop at 2 BBLs I ask, when the sky is really the limit.
As I stated previously, I believe the best solution is to buy a premade 26g stock pot for ~$200, or even a $150 55g drum as suggested, and then cut it down to size, since the OP doesn't want 55g capacity.
It is like getting a haircut- a whole lot easier to trim some off than to spend all day at the salon getting extensions woven in, and don't I know it.
The drums have even better proportions for an MLT than a stock pot, but I would not trust them to do double duty for use as a BK like some do. All the ones I have seen have a gasketed connection for the bottom, or a least a crimped seal with a crevice. There may be some with a keg-like bottom, I just haven't seen one in person.