Tom, when one of my friends was dying he gave me his 2x3 Cambo SC. Up to then I'd shot 2x3 with 2x3 Pacemaker Graphics and had many too many lenses on boards for them. To use them on my new treasure I had a adapter board (mounts a 2x3 Pacemaker board on a 2x3 SC board, size 123 mm square) made.
Along the way and for entirely other reasons I acquired a 4x5 Cambo SC.
When I decided to go 6x12 I made a hybrid Cambo SC. 2x3 front standard, so I could use my lenses; tapered bellows; 4x5 rear standard. Cambo makes a tapered regular bellows for this purpose, I got one. They also make a tapered bag bellows, far too expensive for me then. Instead I sacrificed two lens boards (front, 123x123, rear 162x162) to make bellows frames and made a tapered bag bellows. The shortest lens the hybrid will focus on a flat board is a 35/4.5 Apo-Grandagon. I sacrificed a 123x123 Cambo recessed board to make an adapter to hold an Ilex #3 mounted on a Graphic board with a 60/14 Perigraphe stuffed into the front so I could use it on the hybrid. This is the only recessed board I use. I have a couple of spares, don't anticipate using them.
Doing all this made economic sense given that I had a 2x3 Cambo SC and all those lenses on Graphic boards and the adapter board. If you start from scratch I don't see how you can justify doing what I did. It made sense in my rare (unique?) situation. Otherwise, no.
IMO, if you want 6x12 with movements, the least costly solutions are a Cambo SC-2 (that's the 4x5er) or a Sinar with Graflok back. If you want 6x12 without movements, or perhaps without much movements, go for the least expensive press/technical camera you can find that will focus the shortest lens you intend to use and has a Graflok back.
Good luck, have fun.