Hi to all across the pond from the UK.
I am looking for the data for a
55 Chevy 3100 6 cylinder 3800cc truck.
I need the spark plug,points,dwell angle settings .
Many thanks in advance

Welcome! My first recommendation would be to purchase a shop manual. There's also an on-line option. http://chevy.oldcarmanualproject.com/

Welcome to the best vintage Chevrolet site anywhere!

As per the specs below available at the "oldcarmanualproject":

http://chevy.oldcarmanualproject.com/chevyresto/55041.htm

The point gap and dwell angle are the same setting, as one determines the other and vice versa.

So...

Set your points to .018" or .019", and recheck/reset frequently if they are new points as the rubbing block will wear faster until worn smooth.

Set your spark plugs to .035".

With that you should be good to go!

Many thanks all great info on that .
Is the strobe timing mark the ball on the flywheel

My personal hands on Chev maintenance experience gaps from 1946 to 1960.
But if you are saying you have found a ball on your flywheel... then yes, I believe that will be the mark the engine was originally timed to.
Hopefully someone else here with direct mid fifties hands on experience will verify this.

The engines are not always tuned witH the tIMING set to the flywheel pointer to align with the ball on the flywheel. That is why it is best to have a shop manual for your year engine to find the correct settings.
Also most engines run best, especially on todays higher otane gas, with the timing advanced from the original specifications.
Easy to play AROUD TO FIND THE POINT OF BEST PERFORMANCE.

👍 🙂 Thanks Gene

Probably also a good idea to find your engine ID/serial number to verify what year the engine is.
Just in case it's been swapped out at some point.
Then you'll know for sure what year manual you should be looking in to be sure you are using info for your engine.

Any idea what degree of advance ignition for
95 octane unleaded

With todays regular grade 87 octane is much higher octane than the preimim fuel was in 1955. Higher the octane the slower the fuel burns so you will actually loose power with a too high octane gas.
That beng said advance the timing as far as you can with out engine binding or kicking back when starting......With 93 that will be impossible.
For that engine 87 octane will be more than sufficent.

Many thanks Chevy Nut