Jo Anne,
If you want a vintage Singer with a gear drive and a large arch you should look for a 201-2 or a 15-91. The 201 has the largest arch of them all, or so I have read. Mine sure looks like it too.
If a belt driven machine with a large arch will work, I can wholeheartedly recommend the Singer 66-16 or -18.
They are all great machines, but the 66s just won't quit sewing. I have 8 of them with the ages from 1913 to 1952 and they all sew great. Very well designed and trouble free. Easy to maintain and if the motor dies they are easy to replace. Or you can treadle it. They are excellent treadle machines too.
I don't know anything about Pfaffs so I can't comment there.
Nancy,
What is an "IDT" foot?
Joe