Thanks, Philippe: This partially clears it up for me, but I need more education to fully understand. Does your information indicate that a given casting number can be machined and finished differently to become two different part numbers? Or that either of two different casting numbers can be machined and finished to the same part number? That does make sense. However, the mystery remains--why does my official 1955-58 Chrysler Parts book not list part numbers 1634145 or 1632157? My book does have the 1556156 as the part number for 1955 NY & Imp heads. Also, your note on the 1632157 heads is a little unclear to me. When you say they are for a "ser. 300 engine", is that for the 1955 C-300 automobile or is the "ser. 300" a Dodge truck series? Will both the casting number and the part number appear on each head? Where? I can understand the casting number being cast in with the head and the part number being stamped in with dies. Not to make this overly complex, but it seems I have read that the truck exhaust manifolds have larger passages, are less restrictive and bolt on. Anyone with insight into this? C-300'ly, Rich Barber Brentwood, CA 1955 C-300 Philippe Courant wrote: The "Hollander" shows the 1556157 as a casting number for 1955 heads # 1634145 (chrysler NY and 300, Imperial) or 1632157 heads (dodge truck '55-early 56, 8cyl, ser. 300 engine) The 1556156 is only listed as the 1634145 heads 1323333 is the casting number for 1323334 heads (Chrysler & Imp 51-52 8 cyl, Chrysler & Imp 53 exc those with heads cast.1486833) -- Philippe COURANT (Pau, France) ------------------------ Yahoo! Groups Sponsor --------------------~--> Get fast access to your favorite Yahoo! Groups. Make Yahoo! your home page http://us.click.yahoo.com/dpRU5A/wUILAA/yQLSAA/8LmulB/TM --------------------------------------------------------------------~-> To send a message to this group, send an email to: Chrysler300@xxxxxxxxxxxxxxx For list server instructions, go to http://www.chrysler300club.com/yahoolist/inst.htm Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Chrysler300/ <*> To unsubscribe from this group, send an email to: Chrysler300-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/