You should have no problem using a 75mm SA with your Wista with a flat lens board. I've been usng a 65mm SA on mine for 20+ years.
Regardless of using a flat or recessed lens board there is still a minor problem, the lens coverage/angle of view will include the front of the camera in the image.
However the secret is to tilt the camera, then use the front tilt and rise and the back tilt to place the lens & film plane in the required position. It sounds more difficult than it is, in practice its very quick and easy.
The 65mm & 75mm SA's are superb lenses, very sharp and great performers. The 75mm has good coverage on a 5x4. In comparison the 65mm has a limited image circle and just covers 5x4 with litte skope for movements.
Ian