suggestions for my 340?

When it comes to gearing, the ring and pinion have there ratio stamped on the ring gear. I suggest that in case the last owner has no idea or you can not reach him/her, change the rear ends oil out for fresh oil. With the rear end tires off the ground and the front wheels chocked, place the trans in neutral and spin a tire to see the ratio stamped on The ring gear.

While this is a lot of work just to know 3 little numbers, rest easy to know that your also maintaining the car properly and increasing longevity with the fresh oil.
(You may need friction modifier if you have a sure grip Equipped rear, AKA, posi)