Like Javi, I haven't seen 110 volt lighting in an RV for well over 15 years (unless it was modified by the owner).
One possibility for verifying which was "intended" when it left the factory, would be to look at the wiring in the slide ceiling. Typically (maybe chuckster can verify this if he has access to RVIA standards) all of the 12 volt wiring in travel trailers is single wires that are multistrand, twisted copper wires. All of the 110 volt wiring is ROMEX, solid copper wire.
So, if the wiring in the slide ceiling that supplies power to those "110 VAC lights with old style 60 watt bulbs" is ROMEX, then it may have come from the factory that way. If, however, the wiring in the ceiling is two wires, one orange/white and one white (and they are multistrand individual wires), I'd highly suspect that the original wiring was powered by 12 VDC.
The only exception to the 110 VAC must be ROMEX that I am aware of is the "jumper wiring" that runs from the mobile home connector in the main chassis going to the slide junction box. That is either 12 ga or 14 ga "multistrand" because it bends/flexes with slide movement and ROMEX won't stand up to repeated flexing. I believe the RVIA code requires "multistrand jumpers" for slide AC power.
I can understand why an owner who has his trailer parked on a permanent site would want to remove the 12 VDC fixtures and replace them with 110VAC fixtures to obtain better lighting, but if the trailer is going to be used with battery power, then that renders all lighting in the slide inoperable when "dry camping". If it were mine, the way I camp, I'd want operable lighting when travelling and dry camping, so I'd probably revert to the 12 VDC ceiling lights.
I'd almost bet that the wiring in the slide ceiling is individual, multistrand wires and not ROMEX.
ADDED: Thinking back to 1972 and our JAYCO trailer, we had 110 VAC lighting in the range hood and 12 VDC lighting everywhere else. All of those fixtures used "old style conventional bulbs" but they were 12VDC bulbs and very expensive. I made the mistake of putting one of those 12VDC conventional screwin bulbs in the range hood 110VAC socket and it promptly blew with a loud pop. So, have you verified the power requirement for those "conventional bulbs"??? They may be 12VDC "old style bulbs" that are the same shape and size of today's 110 VAC bulbs. Confusing for sure, but there were (are??) 12 VDC bulbs that look exactly like "standard light bulbs" used in 110 VAC fixtures. Here's one example:
https://www.1000bulbs.com/product/54...iABEgLcNfD_BwE