According to Flaydermans (9th Edition) that serial number was issued to the Second Models, 2nd or 3rd type (mine is a 4th type). Value: $675 - $2000.
I don't know how the Palmetto repro serial numbers ran.
What did the seller mean about the size of the chambers? I have three original .36 calibers - Colt 1851, Savage & North and the Whitney. I use a .380 ball which is actually too small for each gun. A .390 would be perfect.