Here's the block casting #'s and info I've collected..
Please feel free to add the missing & more info also clarify and/or correct any mistakes..
Can-Am blocks 68/69 - Reynolds
# 0-294550 = Linerless?
# 0-321270 = Linerless?
# O-326711 = 4.44" bore with steel liners (427 ci)
Can-Am blocks 70/71 - Reynolds?.
# O-399204 = 4.5" bore and steel liners (509 ci)
# O-495102 = 4.5" bore and no liners
ZL-1 Factory blocks - 1969 - Winters
# 3946052 (No 'O') 427 ci.
ZL-1 Factory blocks - 1997 & up
# 3946053 (No 'O') 427 ci.
# 3992038 (O?) * may be 4.44" bore w/ Liners - era?.
# ? - Yenko - Casting has YENKO
# ? - Yenko - Casting has Y E N K O
# ? - Yenko - Casting has Yenko Crest Logo
# 3946502 is the # quoted on the Guinn's Engineering site but the # is actually 3946052 as shown in their pics..
~ Pete
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I like real cars best...especially the REAL real ones!