Barnfind: Here are some Delco-Remy part numbers for parts on the 734-x starter. Although every car or truck may have had a unique starter number a lot of the internal parts were used through many years on 6 volt equipment. Don’t know why your rebuilder should be stymied by this. Someone who works on 1930’s Chevy Delco electricals would be familiar with this starter variant.
Brush: 811553; RockAuto search gives part # RX30 ; or Ebay or NAPA
Brush Spring: 813521; Rock Auto search = STANDARD MOTOR PRODUCTS SBA4 or Ebay
Brush Holder: 810226; several on Ebay
Brush Ground Lead: 813554; set is on Ebay now or roll your own
Brush Connector Lead: 819362; Ebay or RYO
Bendix Drive: 1855548 ; RockAuto STANDARD MOTOR PRODUCTS SDN17, 12 tooth gear?; also cheaper on Ebay.
Arrowhead catalog equivalent # is SDR5038 (but says 10 tooth!)- search this part number on Amazon. They have it!
Bendix spring: 1855630; can’t remember the antique tractor parts company that carried this.
The Filling Station has Bendix drive screws and lock washers,
http://www.thefillingstation.comLooks like this model doesn’t use bushings, but some type of end plate
Field Coils 1910314 & 1910315 ; some on Ebay NOS; Arrowhead equivalent is SDR4405 for the pair. Don't know who carries this.
Armature 818131; hopefully this isn’t fried; if you need one keep checking Ebay
Let me know if you need more info.
Tom
edit 12/18/18 to add Arrowhead part numbers