You will either run two gear driven cases, or one gear driven case in front of the oem chain case. If you haven't come across the info yet, this page
http://www.marlincrawler.com/transfer-case/line-ups/crawl-boxes/dual-case-unit-v6-mc10-t360 explains what is needed to run a gear driven case w/the chain driven one.
Given that you are under geared for the tires you are running, and not looking to spend a lot, you would likely get more bang for your buck by swapping the 4.56 geared diffs for some 5.29's.
