Have both 8660B and 8660C; I was aware of the thermal issues with the 8660B (I believe it was in the pre-LSTTL era as I understand). It lives in a basement (lowest floor) workshop and fortunately is not on for long periods of time nor subject to ambient above about 70F.
The 8660B accepts regular 60 Hz fan and I ordered a couple of "high speed dual ball bearing 120x38mm 120VAC" fans so that when these things are next on the workbench I'll have spare ready.
As for the 8673D/003, I wasn't aware of the specifics of 400 Hz capable fan; most likely I'll see if I can add supply wires back to the switched 120VAC side of primary transformer (or however the 8673D normally gets power for it's upper assembly cooling fan, which should be revealed by the service manual (which is in competition for the heaviest service manual I've ever seen.)
Thanks again, much appreciate the comments!
