Unfortunately I don't know the original purpose of these capacitors, but if they are designed for mains frequency (or DC) applications, losses at tesla coil frequencies may be high.
My guess would be high voltage DC power supply filtering, or perhaps pulsed power application. Or power factor correction at local distribution level, but there are no "AC" ratings or markings on the nameplates and 64 kV is quite a lot for such purposes, even as a DC or peak rating.
I assume there aren't any manufacturing dates? Do you know when these capacitors were put into use?
Personally, I would not use old rusty oil-filled capacitors that may contain PCB, but you can use your own judgement. Any leak will be rather nasty, especially in the case of overheating (vapor release) or explosion (oil everywhere). Byproducts due to arcing or fire, such as dioxins, will be even worse.
