If your radios have the usual 2 screws per side, make a simple square or rectangular plate for each side, and drill holes to match each radio, spaced by the height you need. Use the top radio bracket to hang it from the dash.
That is the simplest way to do it. If the radios are about the same width, that is. If not, but they're close, consider getting longer mounting screws and some sort of collar to go around those screws to take up the extra space between the less wide radio and the bracket.
BTW, one of the best places to get the metal is an older computer enclosure or hard drive rack. Sometimes, with a little cutting, the plates in those are ideal for things like that. Good luck and 73!