I thought that the different types, eg -31, -34 refer to a different spring tensions within the actuator. I’m sure some one will correct me if I’m wrong.

Personally I’m running a -47 actuator on my Escort Cosworth, as this is what suits my engine specification.

Before my engine rebuild/upgrade I replaced my standard actuator with a -31, and worked fine.

Have a look at to what you have installed, as you should see some markings on the actuator, and make a decision from there.

Cheers
John