Looks like Mitsubishi put propane 2.6's in their rigs too:

http://cgi.ebay.com/MITSUBISHI-4000...185QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Here's a clark with a familiar looking valve cover as well:

http://cgi.ebay.com/2001-CLARK-CGC2...185QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Now I just have to find a parts dealer that might have some scavaged / recycled / unused parts laying around for these.