Look around in the magazines for company called Patrick's. They specialize in the 235, as well as other 6's, and are very helpfull to deal with. Performance parts are easy to come by for the 235.
Also try
www.stovebolt.com
Lots of good links, swap meet, and good bulletin board.
-John
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'71 K-20 350,SM 465 w/33s
'66 K-20 283,SM 420
'59 Willys CJ-5
'48 Chevy Half Ton SM 420
Akron, NY