Get under there and look at it. Some of the features to look for is it a top shift tcase, or forward shift? Does the tranny shifter base have 4 bolts or 6 bolts holding it down? Compare it to these pictures for reference.
http://www.marlincrawler.com/transmission/rebuilt-complete And if you can't get it ID'd, then get some clear and sharp pictures and the guys can help you ID it.
