In searching for a 6 volt battery replacement for my '39 Chief which has a hollow original style battery shell and 14AH lead acid battery, I found a Lithium Iron battery, LFX18A2-BS06, which is 18 Amp Hours and weighs only 1.5 pounds. Dimensions are 4.45" L x 2.28" W x 3.50" H which would fit in an original Indian battery case nicely. Other benefits are that it can be mounted in any position; retains its charge over time (rather than degrading); will not sulfate (big plus for bikes seldom ridden); maintenance free...no water or acid to mess with (or leak out on your rear fender); higher amp rating to push back on generator charging (important for cut-out generators); can be fully discharged and recharged without damage; and can last 8-10 years even with long periods of inactivity. The only "down side" is that they cost $105.00.....about the same as a conventional Indian 29 AH battery, but more than the typical 14 AH drop in modern lead acid battery. Unlike gel batteries they are not sensitive to fluctuations in charging rates found on Indians nor prone to act as expensive fuses when something goes wrong electrically.
Your battery appears to be only a 2 AH 12 volt battery which isn't much capacity and a pretty high price ($80.00) to pay. That would be roughtly equivalent to a 4 AH 6 volt battery compared to the 18 AH 6 volt battery I referenced for $105.00. With an alternator and solid state regulator you might get away with such limited capacity. However, a long wait at a traffic light could literally drain the battery and leave you flat. You need the greater capacity to keep your lights bright, maintain an adequate charge and control voltage in the original Indian 6 volt generator cut out only systems.