The M-42 lens mount was originally from Praktica. Asahi had been copying Praktica lens mounts from the get-go--first the smaller diameter, then the M-42.
Praktiflex was I think a 40x1mm thread (1938) but I do not know if earlyAsahiflexes were the same. I know they were close, at 40-41mm, but I have not tried interchanging lenses.
This is what you are looking for:
Similarly, Carl Zeiss (the West German guys) negotiated
for several years in the late 1960's with Pentax concerning the possible
production of a 35mm SLR camera should the Zeiss Foundation kill Zeiss
Ikon. The fruits of that effort led to Pentax acquiring the Zeiss-designed
K mount and the rights to the Zeiss T* coating, which Pentax marketed under
the 'SMC' label. (This negotiation, while unsuccessful with Pentax, who
didn't feel up to producing Zeiss lenses to Zeiss standards, later shifted
to Yashica and led to the modern Contax SLR camera.)
Vivitar makes a couple of SLR's which use the K-mount. Seem to be decent basic mechanical SLR's, with TTL meter, much like the classic Minolta SRT's. These are listed on the Freestyle and Calumet websites around $150! The Zeiss lenses might be great additions to this camera. I haven't looked at one of these Vivitars in person, but maybe I will. I couldn't find anything on them on Vivitars US website but they are listed on the UK website. Go figure.