That is correct (and is what BIG CHEVY 3600 was saying). The four companies that I posted above used to sell clutch head bolts/screws. A few other might sell some now (like rear fender/box bolts from Classic Parts of America), but new clutch head bolts/screws are not commonly available (and certainly not available in all original sizes).

http://www.jdheritage.net/DeerelyDeparted/Items/7001.asp

http://www.chevsofthe40s.com/detail/10860.html

http://www.classictruck.com/product...erior_Screws_and_Sets_Clutch_Head_Screws