Hey don't think badly of an 8V battery, they work real good if you take the time to set up the tractor for it. Not all tractors can use one though. It has to do with charging voltage. Maybe I can get John S. to write about that sometime. I use an 8V on my HG's, most times I need to turn the regulator up all the way. Your target is 9.2V, the last setup I did came to 9.1V, using a VOM at the BAT terminal on the regulator. A 6V setup runs about 7V. It is pretty easy to see that 7V won't charge an 8V battery, so, after a while, left alone, the performance will drop to that of a 6V. A few years ago someone sent a letter to one of the major tractor publications stating the conversion was a drop in situation, it is not! Nothing needs done with anything but the charging system, the rest will work fine, light bulbs won't last quite as long though, but they are a little brighter. I can't do this on my 70RC, it has a different generator, I can use the 3rd brush to get enough voltage to charge a 12V at 13.2V though, but all the light bulbs had to be changed to 12V. I lucked out and that tractor has a mag, so, I didn't need to change the coil. I hope this helps some!
Take care!!!!
Andy