Below are a couple of tables on 6 volt batteries. The first is a size table vs. Group number for 6 volt batteries. The second is out of PASB 2019-2 which is a comparison of AGM (Optima) batteries vs. regular flooded lead/acid batteries. The full article includes the pro and cons of AGM batteries vs. lead acid.
I use a Group 4 in my Series 36 cars, although this may be too large for your 1930. Part number is Carquest 4-30. Check the table and see what size fits your battery box correctly. My group 4 is slightly smaller than the dimensions in the first table, so it is probably worthwhile to confirm the dimensions of any battery you are going to buy. I think there is probably some difference in size and capacity between different manufacturers.
I have not put an Optima in my cars, mainly because my batteries always seem to fail when the sale is 6 months away. The flooded lead-acid battery in my touring car is 7 years old and still working fine. I do occasionally charge it with a desulfation battery maintainer.