HP6516A with option 001 (High Stability Time Base (TXCO)) and 003 (1 Ghz C channel).

If you're wondering how to switch voltage : you must slide the little cover over the fuse, pull the card (I use a screwdriver and move it left to right the right to left then you can lift it easily). The card allows 4 settings, 2 per face. The selected written value must be written on the left side up. Here is the doc :

(The 003 option adds a third input connector, f = 1Ghz):