I think his main reason for doing this is shallow water use. I guess by serviceable, I mean a boat that can still hold it's own in most typical situations or at least close to the original. If the only issue with the intended use was the inherent draft with the straight inboards, repowering to a single OB of decent size could allow the boat to still function in generally the same way. It certainly won't be any more seaworthy than the original...which wasn't much of a heavy weather boat to begin with.
Moving holding and fuel tanks and maybe even adding some ballast could bring the stability and weight balance back into something that will work. Also, depending on the design of the bracket, it could add some buoyancy to the stern that helps negate the weight shift.
I'm not arguing that this is the best, most efficient way to get to the desired outcome. I am only stating that it is doable, and at this point it seems that kvando is moving forward with the project, so why not wish him luck and hope the work turns out to his liking.
While I do like the old Chris-Crafts, early 80s 28' Catalinas are literally a dime a dozen and it is no great loss to humanity if one them is converted to an OB. In fact, I could see a potential for this to work well...although with limited appeal and no financial gain.
If it is done poorly, it is a lost cause. Putting 25HP on this boat would be a lost cause and not worth the effort.
