I was going to use one of those 5" quad gauges too, but then my son gave me a VERY beautiful set of Antique Beige Autometer gauges. 3"-ish Speedo and four 2 1/2" gauges. I really want to use them, but will have to do some modifications. In case anyone else it interested, this is what I've decided to do:
1. Get the matching 3"-ish tach for the speedo and put them in the original 5" gauge holes in the dash. To do this, I'm going to use sheetmetal cut to fill the holes exactly. Because there will be about a 3/4" ring around the gauges that are left over inside the 5" hole, I was going to use either polished copper or polished brass to accent the brass rim of the Antique Beige gauges. You could paint it the same color as the dash I suppose, but the seam around the adapter plate might look a little conspicuous. That's why I was going to just add to the brightwork.
2. That leaves the 2 1/2" gauges. Best place I can think of to put those is to either adapt the stock grill that goes over the original speaker hole to hold the gauges, or else save the grill and use another metal, such as a sheet of 1/4" polished aluminum or something with the holes cut for all the gauges. Still deciding.
It's custom for sure, but nothing that can't be put back to original if I ever wanted to. If I didn't care about that, I would just weld in the adapters for the speedo and tach and blend it into the dash with body work. If that were the case, then painting it would be best.
