Hello Giles,
I haven’t a clue, but when I remember correctly wrote somebody (maybe Amuro?) that the 5.0 molding version does also fit the 3.0.
Maybe it does on Mk1 too, guess you should simply try it, the normal moldings are not expensive.
Looking at diagram 14 at page 33 of the Strida 1 manual I’d say the moldings are - at least - similar.
Perhaps you unmount your molding one day, we might be able to compare your part with new(er) ones via the dimensions and the location of the seat pin.