[Arran]

 I would go back and replace the 1000 mmf/pf with something closer to a 1250 pf, or larger, values are usually fairly critical, use a film cap don't use a ceramic disk cap. I have read mixed reviews regarding the ready made solid state vibrators, in some cases the manufacturer didn't bother heat sinking the switching transistors, or relied on the copper foil on the PC board for a heat sink, which can cause them to fail,  I bought a kit from WJOE radio for an SS vibrator but have yet to use it but will add extra heat sinks when I do, but I am going to try to get it going with the original vibrator first.
  As to the high pitched hum I can only guess, if one filter cap was not connected correctly, like it was connected to the chassis rather then B- it could cause that, or it could be related to the hash capacitor, I would also look at part #78 the .01 uf across the H.V secondary. Are you running the set off of a battery, a well filtered 6.3 volt DC power supply, or something like a battery charger? I would leave that interference filter alone, unless that 250 mmf cap is known to be paper and not mica, and at 6.3 volts it's unlikely to fail.
Regards
Arran