Wes:
It is interesting that LeBlond told you they did not have information on lathes built prior to the 1950's. When I got my 13" Roundhead Regal lathe, I emailed LeBlond with the serial number. Within 24 hours, Dwight Engel (IIRC) got back to me with the date the lathe was shipped (26 July, 1943) & the original owner who ordered the lathe. I was surprised by the quick response, the fact the original owner's name/city was furnished, and the fact no fee was asked for the information.
This was back in 2012, so not that long ago. Possibly, LeBlond has some kind of vague cutoff as to when their records of serial numbers for their lathes cease to exist. The fact your lathe has a quick change feed/thread gearbox seems like it might have been made at a point in time when LeBlond has some records. I know in the early history of LeBlond, R.K. LeBlond was not solidly in the business of building lathes but was building lathes, other machine tools, other machinery, and parts of machine tools for other firms as well as under their own name. There was a move or two of the LeBlond shops as the business began to grow. At some point, LeBlond became a "stand alone" machine tool builder, and at some point also, they moved onto the site of their main plant. Possibly, your lathe predates the move to the main plant location, and as a result, records might be non existant. Still, seeing the quick change gearbox on your lathe came out of the plant which eventually grew into LeBlond's huge plant.
I wonder if there is some sort of history of LeBlond lathes which would at least give approximate years that things like the quick change gearbox was introduced. Of note is the fact that LeBlond stuck with that basic quick change gearbox design right through the end of the "Roundhead Regal" lathe production (early 1950's ?).
Most quick change gearboxes of this type were "total loss" as far as oiling is concerned. Not enough oil is used to warrant any sort of recovery/recirculation system.
Put the oil in with a pump type oil can and let it drip out the bottom. My old Regal lathe and both of my South Bend lathes are built with "open bottom" quick change gearboxes. This system works fine, and hundreds of thousands of lathes used it, often in heavy machine work or in production shops. Kind of a simple and bulletproof design that has endured until recent years. On my Roundhead Regal's quick change gearbox, there is a note on the thread/feed plate stating that the tumbler lever (the sliding gear selector lever on the cylinder with the holes in it) is to be placed in a certain position in order to oil the quick change gears. There is a cast iron plate on a spring-loaded pivot pin on top of the quick change box. This plate swings to allow access to the oil holes. A few pumps of the oil can as part of the starting procedure for the lathe and it is good to go. On my old Regal lathe, there is a chip pan with a sump for recirculating/flood coolant. The result is all the lube oil which started in the quick change box winds up in the chip pan coolant sump sooner or later. I accept old machine tools as they were built, realizing that while the design might be a few light years behind modern machinery, it worked fine and endured. A few changes here and there, perhaps, but nothing radical.
For belting, you might contact Troy Belting (now known as Troy Industrial Solutions) in Watervliet, NY. Troy is a great firm, and I've dealt with them for over 30 years. They routinely make up belting of all shapes and sizes. Rather than cutting down some conveyor belting, if you have not bought it as yet, you might contact Troy Belting. They have flat belting in various thicknesses and widths and should be able to make up a piece of belting for your lathe with "lacing hooks". These are steel "staples" which form a hinge at the ends of the belt and are joined with a pin (used to be rawhide, now plastic). Belting with lacing hooks is more common than not on machine tools like your lathe and is a well proven thing. The beauty of the lacing hooks is it allows you to install the belt without taking the headstock apart.
I do engineering and machine work at a museum called Hanford Mills here in NY State. Hanford Mills has loads of working line shafting, countershafts, and machinery as well as a water wheel and two steam engines. All of the belting is made up with the lacing hooks, and much of it has been purchased at Troy Belting. We have a "lacing machine" at the Mill and an assortment of lacing hooks so we can make up (or shorten) belts as needed. Glued splices or vulcanized splices on belting are used in places where the little irregularity in the rotation that happens from the lacing hooks cannot be tolerated. Usually, this happens on high speed precision grinder spindle drives or other very high speed applications. The sound of flat belts and the soft "click" as the lacing hooks go over the pulleys (heard mainly on new belting, before the hooks really seat down into the belting) is something I first heard as a kid around lineshaft driven machine tools, and it is a reassuring sound. Like the total loss oiling on these old lathes, belting made up with lacing hooks works so well that it survived to the end of flat belt driven machine tools and is still in use.