could try aluminum flat stock
Our 89 Mac had a bolt that was attached to a slug in the sail track. A washer and wing nut secured the pop top. I never really cared for the design, but it seemed to work okay.
After we lost the slug assembly, we changed the way the pop top was held open. We used two pieces of aluminum flat stock, about one inch wide and 1/8" thick, with holes drilled in them that lined up with the tube support bolts when the hatch was open. The forward end on the straps were connected to the lower end of the front tube bolt with a wing nut and the aft end of the straps were connected to the upper end of the aft tube supports with jam nuts. This in effect formed a diagonal brace on each side.
If anyone leans on the pop top, the mast keeps it from moving forward and the straps keep it from moving rearward. If someone leans on the pop top towards the aft (away from the mast ) the straps are loaded under tension, not compression, and are not likely to bend. Short pieces of cord or small bungee can be used to tie the straps up out of the way when the pop top is closed.
One word of caution: securing the pop top this way does not provide much support against side to side forces on it. Also, you may have to change out your pop top bolts if they aren't long enough. We did.
We liked the diagonal braces better because they were easier to fasten and did not rely on the hatch's front lip made of fiberglass. That said, the fiberglass, if laid up right, could be plenty strong.
One other thing, I had to tell a drunk young lady visiting our boat that the open pop top was not meant to be a seat.....she took it as an insinuation that she was heavy....
Good luck,
Bert
