You can't float the quill on this like you can a Bridgeport or drill press. It is more like the tailstock on a lathe. Furthermore, to put this into perspective -- where the K&T quill travels 0.050 per revolution, the tailstock on my Series 60 Monarch travels 0.250 per revolution, so you have to turn the K&T 5:1 to accomplish the same task.
It absolutely will drill to a repeatable depth. It's a mill. Both the table and quill are graduated to 0.001". There is a spindle reverse. It is a T-handle you pull out located beneath the spindle speed shifters.
You can drill small holes, it's just that you'll have no "feel", so you really need to pay attention to what you're doing and clear chips frequently. When you feed the bit back into the hole, the biggest challenge is knowing when you hit bottom. Yes, the threaded rod extending above the head is a threaded stop and that nut is also graduated 0.001 (0.100 per revolution).
Part of my thinking regarding the head swap is that if you were going to run the BP head exclusively, you are swapping out a 30-taper spindle for one that is R-8 and a head that is lacking rigidity when compared to the machine base. If you can make them easily interchangeable, go for it, but you will be using an engine crane or some such each time you need to do it. The K&T swivel head is more than you can manhandle. I was also thinking that you wanted both swivel features of the BP head and if you do it will move the head very close to the operator. If you sacrifice one, you'll just have to calculate how much of that will be consumed by your adapter plate. The spindle drive gear protrudes from the column a good ways into the head, so your adapter plate will have to be at least at thick to start. All-in-all the original K&T set-up is rather compact. When the table is all the way toward you the centerline of the K&T spindle will not move beyond the rear of the table, so any distance you move the BP spindle toward the operator is table travel you will sacrifice.
I mostly get by with my 2HL and drill press, though there are times I wouldn't mind a Bridgeport.... and about a 1/2-dozen other mills I would like to own! I recently added a 2D so that did away with the need for some of the others, though in my case a lot of this stuff is more to do with "want" than "need".
Years ago I made a post about servicing the head and the photos are gone since having divorced my photo hosting service. My intention is to redo the post as soon as I can find another good way to host the photos. If you haven't bought this thing yet and the seller will let you, remove the nuts one at a time, remove the washers, then slip the nuts back on about two turns and pull the head back so you can have a look at the wear on the spindle drive gears. They don't run in an oil bath and are often neglected. Also, you can pop the quill feed handwheel assembly off rather easy by removing the socket head cap screws, though I doubt there is much wear at that location. A third potential issue is the quill clamp collar seems to be a point of neglect. My is broken and I have seen another like that. It's easy enough to check. If you clamp it and the quill still moves as though it's not clamped at all, it likely has a busted ear. Otherwise, as with all K&T's, check all the feeds in all the speeds and make sure the rest of the works are in good shape.