Original standard RST boost pressure was 7.25 PSI.

I am unsure what you mean by 'serial'?!

Do you mean how long are the visable threads on a standard actuator? If so, I have no idea!!

If it's the original actuator or a very old actuator, you would be better throwing it away and getting either a new one or a -31 as the springs go weak. It could be that the tension has been wound up to try and compensate for a weak spring.