SBC 350 - spark plug question

[chrislehr]

I went to O'reillys and picked up 8 of the Champion RJ12YC about 3 mos ago.


Today I go to put them in - they don't fit! The "base" is too wide.

So I take out one existing, an Autolite 26.

Now according to Autolite's site, this make/model should use the Autolite 303. But that one has a fat base too. Are my heads non-stock or something? How can I tell?

So I ended up buying 8 more Autolite 26's. Product sheet here:
http://www.power-21.com/honeywellpow....aspx?b=&pn=26

Now, the real fun. I get home, swap all 8. Only one of the PO's was an autolite. All the others were AC Delco R45TS plugs.

So I guess the question is... do those wide base plugs fit in other SBCs? Why not mine?