Hey,63
I believe I have read on this page that short beds from 55 to 66 are the same. Check the catalogs for new bed strips. If the 55 to 66 are the same part number, then the bed supports are in the same position, and you should have a perfect swap. I bought a mid-80s short bed for my 57, and have no doubt that it will fit just fine, after changing the fenders. Any misinformation in this message should be corrected ASAP.