Is 355 gears as high as you can get for a Dana? Any 323 gear?

Don't think so. I've only seen 3.54 for danas.

There were 3.07 and 3.31 gear Dana 61s. Pretty much identical to a 60, they just moved the pinion over a little.

I built my Dana for my car out of a 1979 f250 3.31 gear Dana 61. Used a 3 series (4.10 and down) 60 power lock in it with no trouble. All the bearings and stuff were the same as a 60.

I've read about a 3.33 gear for the 60, but couldn't find any or even if they really even existed

The Dana 61 3.07 gears can be used in the Dana 60 by using the 3.54-4.10 differential and removing material from both the ring gear and the differential flange where the ring gear mounts....some even remove material from the bearing flange to move the differential over. Sources for the gears listed below:

FORD REARS

603438-6 F-250 1974-75

603713-5 603714-1 603540-5 603899-1 1976-78 F-250 4X2

603594-19 1975-78 E-250 (VAN)

603925-1 1979 F-250 4X2

603932-7 1979-80 E-250

603946-1,2 1980-81 F-250 SEMI-FLOAT 4X2

605022-10,12 1981-83 E-350 DRW CHASSIS

605039-5 1981-83 F-350 CHASSIS

Nobody makes new 3.07 or 3.31 that we could find.
Doug

On the off chance there are some old stock Dana 61 gears still floating around, here are the Ford numbers I have:

For the 3.07

D8TZ4209F
D0TZ4209E

For the 3.31

D8TZ4209D
D9TZ4209B

I believe I have a set of the 3.31 if someone would like a set.