I noticed that the 72 DT2 parts bike I picked up has a larger battery & battery box then my 71 DT1-E. Is there any advantage to putting the larger battery in my 71? I also noticed that there is a round item attached to the battery box that looks like it might be a flasher unit. Is that what it is?

Thanks

Most likely, yes.

Assuming that it's not faded, there should be some writing on the opposite end from the wires/terminals, including something like Nissan Denso (or ND) 6v 21w x 2 + 3.

I have a '73 battery box in my '71 with the Motobatt MBT6N4 absorbed glass mat battery. Need to file small notches in the sides of the box to make sure the leads don't rub on the box. Doesn't leak and lasts for years.