Update: not a lot of used beams around. Looking at the blank tubing route. I can't measure wall thickness accurately, but it's a little more than 0.0625, and one source I have suggests 0.078 (5/64t) which apparently is an odd size. Thinking about going up to the common 0.125 (1/8in) and filing down the compression tube a hair to fit. Waiting on a quote for a stick of this stuff (4in OD) and I'm sure I'll almost fall over when I hear it.

Dolphin striker rod: trying to get around the $70 buying a new one, but custom making one mite be too expensive (I don't know any hobbyist machinists). Apparently 9/16th is an odd size for stainless rod, on top of the fine (18) thread. Damn sailboats!

V-strap: looking at either welding a brace over the corrosion at the centre of the V (isolating potential cracking and the mysterious drilled hole) while also acting as a dolphin striker rod casting. Or ordering the flat bar and bending a new one. Talking to a shop to figure out what alloy it is. He thinks 7 series (bendable, not very weld able) so may not be able to fix old one.

Oh, and to top off the weird sizing of all the materials (apparently this is deliberate by many manufacturers so that people have to buy original parts, not make them like I am) the trailer steel (channel) is an odd size, so I can't match it easily. Not that I care to much about that, since I'm not trying to fit anything to the old frame, just adding across the top of it.