Marklin H0 Hobby Car Lego conversion.
Part with Lego compatible studs on top that fits to a standard Marklin Hobby range chassis on the bottom. It reuses the original locking system so no glue required. Make sure you keep using the original metal plate for weight.
I used this design myself to reuse a chassis whose upper half had broken off.
This makes a nice 2-axle car that fits nicely together with the 4-axle car that Marklin sells.
I used 4mm brim and Cura to slice. Foto shows a print using stock silver Prusa PLA.