I pulled the original 2.56 & worn out cone posi to 3.55 earlier this year. Purchased new eaton posi and Richmong gears from these guys on their e-bay store: http://www.rearendparts.com/

If you have 3.36 gears you are dealing with the 8.2 BOP. You need to change the carrier if you go numerically lower (although I've heard you can get adaptors). I do not think anyone makes new 3.36 gears. Only new BOP gears are 3.55, 3.90 and up.

3.55's with TH400 is a blast of the line, but not much of a highway cruiser. Mine revs about 3200 @ 70 mph. Overdrive would sure be nice.