Update; The solid-state modules in this post created a voltage drop that I felt was unacceptable. They were replaced with Bosch-style 6v relays which work very nicely with practically no voltage drop. Details are in a post further down this thread.
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For reasons discussed above I rolled my own relay harness in the 6v P15, still using the halogen sealed beams but may upgrade to the Toyota H4 reflectors. I post this in case someone is interested in doing something similar. The relays are solid-state devices available from the usual sources at very reasonable cost. I used 12g wire to carry the heavy current inherent in the 6v architecture and kept the runs as short as possible.
Are the lights brighter? I don't know, haven't taken any comparison readings. But I like how the light and dimmer switches are now relieved from handling the total headlight load and the risk of overheating (or worse) should be practically eliminated, especially with the LED tail, brake and signal bulbs. Also, the low and high beams now have direct fused feeds from the battery instead of the single fuse on the headlight switch carrying the total load and being a single-point failure. Hopefully this will be an upgrade that will prove to be reliable, time will tell.