BGreene...when I put tabs on my 21, this is what I did to fit w/the swim platform...relocated the bracket from the transom to the side of the splashwell and notched out the platform...worked out well...
Thought I had a close up pic, but this best I could find...
Here's the same solution, only on my old '74...
Kept the SS frame and discarded the old plastic deck...remade out of 3/4" Starboard to fit...