Jack,
Due to the size of the front of most 4x5" cameras I don't think adapting an FX or smaller dSLR will be that useful. If you are shooting Nikon then I'd recommend a Nikon PB-4 or PB-6 bellows. There are also various medium sizeed systems with significant front standared movements that are probably more appropriate than a 4x5 camera. Note that the depth of the mirror box can easily cause hard image clipping.
Years back I made an adapter for a Pentax 6x7 body to Linhof Karden Colour 45 S monorail view camera. I also have an unfinished Graflock 4x5 to Nikon F adapter. I could use it with a Linhof Technika IV for extreme bellows extension but it's unfinished.
You might make an adapter for the baby Grafix. I owned a 6x9 Century Ggrafix and it folded up nicely for hiking. I traded it for a Technika 45 which also folds up nicely but weighs about as much as a millstone.
Best,
Dave Hartman
Sorry about typos: this phone changes words and my spelling socks.