[D Cassidy]

Hello.
Motor run capacitors are not rated as X types as such as they are designed for a different purpose in life. In a Radio they are under considerably less stress than in a motor so have a long life. One proviso though is to use ones rated at 400 VAC.
You can use two caps, one for heaters and one for HT. Yes and with half wave rectified HT. Ideally you need a valve HT rectifier that has its Anode connected to the supplying capacitor dropper. Then also from the valves anode a silicon diodes cathode connected to it and the anode grounded, a 1N4007 is ideal. This actually works like a doubler so the valve rectifier is essential as the HT could rise over 400v with silicon in both positions. The value of the cap dropper will only be about 1uf for HT using this method, dependent on HT current.

Doing it that way will ensure you have the chassis at neutral and not floating at near half mains.