John,
The tubes are rated at a total of 1000 watts dissipation, so I'd say if your
input is 2kw and output is 1 kw you are ok.
The power supply might get a bit warm but I seriously doubt that it would fail
under these conditions. I hear that the electrolytics fail often in L4Bs at
about that age, so the heat in the PS might not be good for aging caps, so now
might be a good time to change them.
If you are ragchewing you could back the power down or maybe use the low
voltage setting, but for contesting you probably want all the power and dbs
you can get.
By the way, I have one here also and I need to get in there and change my caps
too. I recently added a transistor swiching circuit for the antenna relay to
make my transceiver happier.

Rick K2XT