They may work, doesn't the square bezel just come off of those? I have to figure out how Formula set the dash panel up on the newer ones to make them look flush mounted. I'm thinking there are 2 panels, one on top one below? does anyone know before we pull it apart?
FWIW, VDO still makes those gauges I think. You won't find them easily on any websites but a quick call/email to Formula TAG (Tech Asst Grp) should get you Formula part numbers and possibly VDO part numbers. As gauge prices go, they weren't terribly expensive (under $100 for tach w/digital hr meter).
TAG should also be able to advise on how they're mounted. Not sure if you can just remove the square bezels for flush mount.