You have been busy!
I wouldn't cut any of the fibreglass to inspect the steel, you'll see any issues upon close inspection. When the steel rusts it obviously expands and blows out the fibreglass, so if it looks OK it probably is OK
Mine was shot just about everywhere, it wasn't garaged like yours, and obviously a bit older...
The pedal box is a bit of an issue on the Marcos, as fibreglass is obviously thicker than steel meaning things don't line up very well. Plus the bottom bracket of the stabiliser is a bit of a fudge, as we can see from yours! - I've added quite a lot of additional fibreglass strengthening to my shell, thus making the fit of most things even harder. And me therefore having to modify, or fabricate from scratch a lot of parts.
But going back to the rust, hopefully yours doesn't look like this
And the replacement...
Edited by Rebuild in Progress, 21 March 2024 - 12:35 AM.