Thanks for all that info. It was very helpful in my mods.
I just upgraded my 111w153 to a large bobbin with a heavy thread B1830563BA0 hook. The hook cost all of $20 including ten bobbins! It's actually a surprisingly high quality, made in Taiwan unit and works perfectly. The machining of the saddle could be done on a decent drill press equipped with a square end mill and either an inexpensive cross slide or a thoughtful reposition-able clamping set up. Just set your depth stop and carefully chain drill 0.1" off of each land. I happen to have a milling machine so it was easy for me. The machining of the case opening lever arm "trough" does expose a set screw (make sure you remove it before you start) but on my saddle, the shaft to bore was such a tight clearance, I didn't move the set screw. I simply carefully tapped the shaft back in. The arm is under so little load, I am confident it will never move. I thought of applying some retaining compound but the risk of getting in the shaft clearance and gluing the arm to the shaft is too great.
I also modified this machine in several ways to match the specs of a 111w155 with regards to the lift of the presser foot and the height of the vibrating presser foot. I believe these 111w machines are all basically made from the same casting. If you want to do this, with the exception of the pocket on the main casting, you can replace parts or modify them. The pocket could be milled out with a square end carbide die grinder.
This is the parts list and required modifications:
Presser bar lifting bracket: I milled the Presser Bar Lifting Bracket "pocket" to match the specs on the 155, which allows the same lift of the 155 if you install or modify the requisite Presser Bar Lifting Bracket. The modification requires machining the top part of the main arm to clear the end of the take up arm shaft. This could be carefully machined with a grinder or a die grinder.
Presser bar bushing (lower): The presser bar bushing (lower) can be cut off in place, removed and turned shorter or pressed out and replaced. I estimated that the 155 unit is about 1/4" shorter. This could be done carefully with a hack saw, just make sure to deburr the edges when done.
Tension release slide (optional) This can be replaced but the 153 version seems to work regardless.
Presser bar lifter (optional) The 153 version also works as-is but the 155 unit will lift the presser bar higher.
Is this a lot of work? Not as much as you might think. Most of it is disassembly and re-assembly and if you do a clean up of your machine at the same time, it can even be economical. For those of us with more time than money or who do this as a hobby, it may take less time and money than looking for, buying, shipping and moving a new machine.
Next up, installing the adjustable lifting eccentric singer number 240744 or 237196. https://www.bmfwholesale.com/product/eccentric-singer-number-240744-237196/