This picture is from your website... Am I looking at this right? It looks like a plate was used to seal up the transom where the lower units used to be and then surface drives were bolted to the plate. Is this a good idea? Does it work? And if so was a plate used on the inside too ?

That boat had BMAX drives on it with Yanmar 440's and they could not make it out of the Harbor

They (US Navy) just plated over the cutout and that's what you see. You do not need anything on the inside as the plate is 1/2" thick aluminum. Just seal it up and go again for the diesels. Gas engines, the Conversion kit removes the need for this.