here is the link for the ISMACS singer model listing for models 1-99
http://www.ismacs.net/singer_sewing_...sses-1-99.html
model 78-3 says
"Walking Foot - One Needle. Max. speed 1600 spm. For lightweight work in imitation leather; upholstery. Automobile tops. Combined upper and needle feed. No under feed."
and it uses needles "16x99; 16x100; 16x198"