No, never seen another frame with that horizontal slot/slit. I'd love to ask both Legrand and Serier a lot of questions about their approach to frame building, but alas, I've heard they're not open to that kind of thing. both can be met 'accidentally' in a bikeshop in Amsterdam that I know, where they sometimes walk in for a coffe and a chat. But not about the old days! I've read a story about Legrand in the excellent semi-literary periodical 'De Muur', which was all about his love for jazz. In the 60s and 70s he must have met famous jazz players like Chet baker in Amsterdam. Now music matters more to him than stories about the old days.

I think (oh, forgive me, maybe I'm rambling now! Can't stop ...) Presto's were really the pinnacle of frame building in Holland: a 'to the point' approach, combined with understated artistry, as is shown in those details. No frills, just a race frame. I think (but have no way of proving that) those details were not discussed with the customer, just decided upon by the builder. Mmm, OK, I'll give this big frame some holes in the headlugs, makes it a bit more elegant ...

Last year I had a chance to talk with Frank Hoste (Belgium), who rode for TI-Raleigh in 1981 and 1982 (won Ghent-Wevelgem in 1982, so better watch this weekend.). So I asked him how Jan Legrand went about making the frames for the team members. Did everyone bring his own notes with the dimensions/geometry and gave it to Jan?
Frank told me that, as Jan was team mecanic, he would just look from the team car at the riders during the races, make some notes on what he liked or didn't like, build a frame in the next week that was just a bit different from the present one, build it up and gave it to the rider in question: hey, ride this! Not too much communication going on there ...

Marty: not only should I get a Peka (but where can I get one), I should get a Gino too .... (Cycles Gino, small bikeshop in Amsterdam, long gone ...).