Joe, I'm not trying to make this personal but have you ever torn one of these apart? I read some parts of your post that seem intelligent and speaking from experience and then others that make me question if you've even seen one torn apart, much less done one yourself.
The felts take the form of "wipers" mounted on the ends of the carriage wings.
That's not the felt I was referencing.
I believe there may be felts used in grooves to make a seal between the carriage and the saddle.
NO NO NO NO NO... that groove is NOT for a felt to be placed in, that is an oil passage. Inside that groove there will be several holes drilled to various moving parts of the apron. On the mating part of the saddle there are hole drilled that are open to the groove, the oil is pressed up out of that groove into those lube holes to lube the cross slide screw journal and a larger hole the leads into the saddle way lube passage. All of my rotating shafts in the apron have lube passages from that groove to the journal/bearing as well as tiny copper lubrication lines from that groove directed to the small reservoir on top of the half-nuts. DO NOT put felt in that groove, it will block lubrication to those parts. Rather, the holes drilled in the bottom of that groove should have felts (1/4" diamter round) placed in the bottom to keep the lube from completely draining out of the groove (it acts more like a slow drip of lube to the shafting in the apron.
Coat the mating surfaces with some of the oil you'd use in the headstock (DTE Light, or ISO 46) and put things back together after stoning the mating surfaces.
They may have precision fit early aprons but later aprons were gasketed from what I know. If OPs has a gasket when he takes it apart I recommend he use a gasket when he puts it back together.
In taking things apart to separate the apron from the saddle there should be dowel pins. Dowels can offer some resistance when you go to take things apart, so the apron and saddle may not just separate once the capscrews are out. Do NOT get frisky with a pry bar if you encounter resistance in separating the apron from the saddle.
The being careful part is not bad advice, but my late-model (just before the switch to square-heads) does NOT have dowel pines of any sort in the apron/saddle so don't be alarmed if they aren't there.
Before you get into dismantling the apron from the saddle, I'd suggest you fill the apron with some kerosene and maybe some Marvel Mystery Oil and start pumping the oil pump plunger.
Joe, this is bad advice, STOP giving it.
As I stated, the groove in the apron leads to passages that go to shafting in the apron. Once the gunk is pumped through and gets in those passages you won't get it back without a 100% teardown of the apron. If the plunger is gunked up enough to be sticking it has enough gunk to plug up oil passages or worse. Best case scenario, if you pump the plunger to flush kerosene through the system is that the felts are in great shape, they filter out the gunk that WOULD have gone to the apron parts, instead sending it all to the saddle parts (that way you only have to tear the saddle apart to clean it out). There is nothing good that can be accomplished by breaking up the gunk in the apron and pumping it into oil passages unless you're just looking for a "hack" to get the lathe in service with no regard for longevity of the parts.
I wind up sticking a funnel with a flexible spout into that Gits cup and pouring in ISO 46 oil when the pump starts making the "slurping" or breathing sound. This is my clue that the oil level is low in the apron.
Wouldn't the oil level in the gits oil cup be a better indicator? That's where the oil level is supposed to be, don't wait until you hear sucking of air, by that point the oil level has dropped low enough that the oil lubricated gearing is not in as much oil as it is designed for.
There is a drain plug at the bottom of the apron, so you can flush the apron and satisfy yourself you are not pumping sludge up to the carriage wings and cross slide. I tend to try to go for the easiest approach first and not make more trouble than I already have.
The carriage wings and cross slide are not the only place the oil goes.
Also, that drain plug in the apron is located directly across from the plunger, pull the drain plug out and the plunger and spring should push out the back side of the apron.
BTW I have heard that the roundhead regals had hardened ways, and mine are pretty nice feeling, however other areas on the bed seem to have been flaked and have long since worn through the flaking. When I am comfortable that everything is nice and lubed I'll turn a steel or aluminum rod and see where I sit for nonlinearity.
Late model round-heads had hardened ways for the carriage (cast iron for the tailstock), early models were cast iron for both carriage & tailstock. The tell-tale sign: If you have inverted vee ways for your carriage they're cast iron. If you have flat ways for the carriage (the front one is angled ~20 degrees) you have hardened steel.