There are plenty of drop bases available, most are based on a 14" air filter... I wanted to keep the stock Mopar 13" unsilenced air cleaner top so I used the bottom half of one of these Ford Air cleaners...Only a 5/8" drop but it does what I needed...

http://cgi.ebay.com/ebaymotors/1965-1995...d=p4506.c0.m245