There is a military manual that goes into detail on the various Clark transmissions. It is TM 9 - 8611.
Sometimes you can luck out and find a freebie PDF download if you look enough.
These guys have one for about $11, which is not bad. I have purchased downloads from them before, and their quality is usually very good.
TM 9-8611I have the paper copy. It has a chapter dedicated to transmission identification (Ch 6) , but it basically says look through the book and see which picture matches your transmission
.
Clark made a many different models of transmissions. It looks like the top cover with the remote shifter mechanism can be refitted to most of them. Yours kinda looks like a a 204VO - but there are several differences between the 204VO and your transmission (see the pic below for reference):
1) The shape of the your cover is different, and does not have as many bolts as the 204VO.
2) The PTO cover on yours is almost perpendicular to the ground, as opposed to being angled on the 204VO.
3) There is no bolt thru the case on the left side near the top for the 1st/reverse lever.
4) The trans just looks "shorter" than the 204VO.
In looking thru the TM, it seems to more closely match either the 185F, 186F, & 187 F series, or the 230F, 231F & 233F. These are all 4 speeds.
BTW, when there is a "V" and "VO" model, the "O" designates overdrive.
As you have found out, you need to double clutch on upshifts, and double clutch and tap the gas on downshifts. When I drive my truck, I can hold my own on upshifts, but my downshifts are still a little shaky. As for shifting sans clutch, as Jerry mentions, I have a looong way to go before I can try that.
Hope this helps.
Best Regards..
