It is a CTC12, and does not have a UHF tuner built in.

There was a kit available from most manufacturers to install a tuner in the knockout in the front of the cabinet, and the tuner may or may not have an IF input on it for that tuner. If it does, the UHF tuner will have one tube, a 6AF4. If it does not, there will be a wafer switch that mounts on the back of the VHF tuner to switch the IF link to either the VHF or UHF tuner, and the UHF tuner will have an IF amp piggybacked onto it that uses two more tubes.

Because there are antenna connections on the back cover of the set does not mean they are connected to a tuner inside, and probably aren't.

I've seen a few of those installations!
I couldn't see why RCA didn't include an input jack in their VHF tuners, like they had in their all channel sets. It would've been a lot cheaper.