First, the 12" tailstock doesn't have a riser. The casting is just 1" taller than the 10" one. Both use the same 10D-6 base. However, the tailstock only has a single web at left and right side. It looks like the ones off of the 12" and the 10D and earlier. All of the known 10F photos have one on the left and two on the right. Please measure the vertical distance from top of bed to center of the ram.
While Serial Number 1053 is consistent with late 1948 or 1949, the "D" in front of it would mean that it is off of a 10D from about 1937. How about adding a photo of the leg under the tailstock end of the bed?
The belt cover looks like the one off of the 101.07383 and none of the catalog photos up through 1952 (which is the latest catalog to turn up) show a smooth front headstock with the quadrant for the three indexing holes for the FWD-OFF-REV tumbler cast into the headstock. Both of the parts manuals on the three known QCGB models show either a bolt-on quadrant or no quadrant. So if it is a 10" headstock, you lucked out. Also, all known headstock photos from 1942 on show a rectangular area pushed out of the front of the headstock onto which a rectangular plate is attached to hold the original bat handle toggle switch for the motor. That isn't really an issue, though it does hurt the identification.
Does anyone else here have a QC model that has those index pin holes as part of the headstock casting??
Finally, although I haven't any current sources for spindle bearings, the fact that you stuck the word "reasonably" in front of "priced" pretty much guarantees that you are going to be flabbergasted when you get a few quotes. Most new owners of old lathes (regardless of badge) seem to think that just because the machine is old, the prices for new parts are still going to be old as well. Unfortunately, prices for new parts are going to cost what new parts cost today. Attached is a PDF file showing the Timken numbers for the bearings (this file is also available in Downloads but because of what it costs us every month to store files and photos, access to Downloads requires Donor status).
On the questions about the Compound Slide, yours isn't a 12" as on it, the mounting surface for the tool post, etc., is raised above the rest of the slide by about 1". Yours looks like a standard 10F slide that someone has carefully ground down the top of a little. Normally, the flat surface for the tool post is just a little lower than the top of the original casting, and new owners who mostly quickly add a QCTP (Quick Change Tool Post) find that they must machine the flat farther towards the rear in order to install the TP properly. So the good news is that it may have already been done to yours, although it still has part of the lantern style TP present. And otherwise, aside from missing the two square head lock screws and probably the beveled locking pins plus the lock nuts on all of the gib screws, the compound slide looks OK.