It's going to be 4 1625's modulating either 1625's or 4d32's.
You can't go wrong with four 1625s for modulators. I modded my Valiant to use four 1625s in push pull parallel. I replaced the entire speech amplifier, UTC A-10 input transformer with XLR input connector to connect to the audio chain. Gain stage, phase splitter, and 6SN7 cathode follower driving the 1625 grids. I used a UTC 120 watt universal mod transformer, and the original valiant mod transformer has all windings in series as the heising choke. Heising capacitor is out of a dead microwave oven. Solid stated the power supply, leaving room for all those mods above chassis. I thought of replacing the 6146s with a pair of 4D32s, but I decided to leave the RF sections alone. But a pair of 4D32s moded by four 1625s would rock!
My valiant includes antenna switching relays with a solid state sequencer, and N connectors for antenna and receiver. Edit: I almost forgot, it also includes Steve's QIX 3 diode negative peak limiter circuit.