Just pull the shifter boots and look down to the top of the trans/tcase. If the tcase shifter base is right behind the tranny shifter, in the top of the trans its a forward shift case. But if the tcase shifter mounts to the top of the tcase, then its a top shift case.
Here's a top shift tcase
Here's a forward shift case
But if the trans is original, the tcase should be a top shift, since the L-series trans only came that way. But if it does have a modern trans and a forward shift case in it, thats no biggie, since all you need to do is swap out the shifter rails.
http://www.marlincrawler.com/transfer-case/shifter-parts/top-shift-conversion-kit
