NAA shift rail oil leak

I'm rebuilding the 4-speed trans on a NAA. Trans is largely assembled, and still sitting on my stand. Customer gave me a jug of 80W-90 gear oil to put into it. Since that's what the repair manual calls for, I went with it (I realize that the current NH recommendation is 134 hydraulic oil). I filled it to the bottom of the check plug hole and then noticed oil leaking out past the shift rail.

According to the parts book, 4-speed transmissions built after the NAA (e.g. 600) have a cap that goes over the back of the shift rail. Since the NAA trans case is not machined for this cap, I don't have the option to install that. I'm thinking that since my shift rails are grooved, that this is why it's leaking so badly. I also suspect that my shift rails are from a later transmission, since Ford would have had no good reason to groove those rails prior to the introduction of the sealing caps. What do the experts out there say? Most of my Ford tractor experience is '65-up.

I don't know of any other solution short of finding shift rails with no grooves in them. I'm thinking it would be easier to simply convert it over to 134. Would you remove the output shaft seals as well in this situation?

some used gasket that went around hole cause r/a hsg had hole for rail to go in to

I don't remember the reverse shift rail being groved are capped.
I have been into quite a few 8Ns and one 600 they are basically the same. John Smith would know he's the man...

http://www.oldfordtractors.com/2gears.htm

I made this post and John upped it with a better one..

http://forums.yesterdaystractors.com/viewtopic.php?t=359528&highlight=bent

Boy, do I feel stupid. You're right, the rear axle housing has cast in holes to seal that area off. Thanks for enlightening me!