Hi Ian, very late on this and you may have resolved it by now but maybe worth saying anyway that the telltale on a '32 9A does not open the oil supply to the rockers. If you look, the rocker feed is permanently open, it's the big end feed that opens under pressure. This is the same as on older Sunbeams, acting as an anti wet sumping valve to prevent head of pressure in the oil tank causing oil to leak from the big end. Being higher than the oil tank, the oil can't drain into the rocker box in this way but there is a restrictor jet in the pipe elbow on the rocker box to ensure enough back  pressure to open the telltale and feed the big end.
Rather than copy another spring I would mark/measure the plunger so you know when it is far enough out to open the big end feed and fit a spring that allows it to  do  so at all speeds/temperatures, because that's really what you need to know and I've seen some oddities with telltales - too many sealing washers, home made plungers etc - that may mean a 'standard' spring wouldn't work.
The gauge is useful because it should warn you that the crank feed isn't open by showing higher pressure than normal while if the crank feed was stuck full open you may get no reading at all.
Cheers Ricik

Hi
I am coming to the end of my Sunbeam rebuild and have another question/request.

I appreciate the topic of telltale springs has been discussed many times.

As the oil is the life blood of the machine, I would like to confirm the telltale spring I have is correct in length/compression to do it job of diverting oil from bottom end to top end.

The only way is to compare the two springs I have is with a known working example.

My location is Cheddar Somerset, is there a 9a owner in the vicinity I could make this comparison or could I post my telltale springs further afield.

Thank you for your posts assisting me in the past.

Regards Ian