Ok i will take a shot at actually answering your question. the problems i see with the swap your talking about is the 2nd shift fork and the counter shaft bearing.
To do the swap from ka tranny mated to the L6 bellhousing you have to bore out the countershaft bearing hole and you have to bore out the 2nd shift rod hole to 5/8. So when you go the other way the countershaft bearing is going to be to small for the bellhousing. Granted its an easy fix with a bearing swap but the bearing isnt cheap and you have to order it from nissan and it runs like 50 or 60 bucks if im not mistaken. Now on the 2nd shift rod your rod is going to be to small for the hole in the bellhousing. now you could make a bushing and put it in the bellhousing to make it work but unless you have a machine shop yourself, your spending more money again.
So to answere your question the answere is yes it can be done but your going to end up spending probably around $100-$150 in parts and having stuff machined. so why not just get the sr tranny that can be had for cheaper. I know i can find ka24de trannys all day long for 100 bucks.