JoeJr

I promised no more thoughts, but technically this is to LeonF. I have a 15-90 and 15-91 in the garage, and although making a 91 into a 90 might be possible, it would require finding the bobbin winder/belt guard assembly for a 90 which mounts into the same holes as the potted motor on the 91. The handwheel on the 90 looks standard and mine has the tri-pole plug so there is a specialized bracket to hold that and the motor. It looks as though you can remove the tri-pole plug assembly from a 91 to reveal a standard rail mount. I haven't taken these apart just now, but going from memory when I had the respective machines apart for cleaning.

But Leon's idea is worth digging into further.

bkay

I'm not a very good sewing machine mechanic, but I don't think it's probable that you will find a motor that will fit that housing. Instead, I'd find a Japanese mid-century model that came with a 1.5 amp motor, or I'd find a 66 and change it to a 1.5 amp motor. Also if I remember correctly, some of the vintage Kenmores have the 1.5 amp motor.
With the 66 or Japanese machine, you can use an existing table. Not so on the kenmore.
bkay

Hooligan

I own, use a 15-91 daily and curious as to what projects your undertaking and what your expecting from the machine. Very rare in my opinion for the 15-91 to complain with what is thrown at it. If it fits under the pressure foot, the correct needle fitted with a well maintained/adjusted machine then it will sew what you want. Maybe you just need to make the jump to an industrial???