Pulley Bolt pattern- 340 harmonic balancer

Got a 1968-340 and trying to order single pulleys for the harmonic balancer & water pump but i want to make sure i know what type of balancer i have.

If it still is the stock 340 balancer, it should be internal balance, i assume it is... but one of the pullies i had i thought was from a 340, didnt match up.

I know the 360 used a different bolt pattern on the lower pulley.

Is there a casting number, way to identify or measure bolt distance?

I hope there is a casting on my water pump because its a passenger side dump, so i think thats a 1970's pump that measure different at the pulley offset than a 68 pulley.

Thanks for any help