Re: Finally nailed it down to one choice!!!!
TJB--
yes, those plastic inserts were for a factory bimini top. but AFAIK, aftermkt biminis don't mate with those bases so you'll prolly just want to remove em.
you can mount an aftermkt bimini either to the flat surface on top of gunwales or to rail if you have a sturdy horiz rail in right place. the factory top on my 64 Starchief (sorta like an earlier version of your boat) mounts on the rail. for same height bimini, rail mount will put the sun-heated top further above your head and feel "airier" but will let in more low-angle morning and late afternoon sun.
bimini will extend roughly same distance in front of and behind the mounting point so decide where you want the shade to be, and that it will clear your windshield etc. Standard top lengths are 5, 6, and 8'. Anchoring straps extend fore and aft from the bimini and will interfere with fishing rods so take that into acct. different quality grades of biminis available, as to both top matl and frame sturdiness....i plan on adding one of the very sturdy stainless fitting/doublewall tubing ones because it will also be a grab rail when i'm climbing up to bow with a fish on.