Today I stopped the local autoparts place and picked up plugs for my '89 454 Mag. R43TS (couldn't get the MR and right now just testing). So I get home and go to change the plugs... find that it has Autolite AR3934's instead.

Major difference in plugs! The Autolites are a 14mm 3/4 reach with a very strange ground strap. These plugs are similar to the plugs used in my aftermarket heads (Brodix - 355 small block).

The heads on my boat were replaced by the previous owner back in 2007. The work was done by a Merc dealer up in Maryland. Do I have later model heads? Any ideas on what's going on?

Anyone?

I looked at the paperwork when I got home last night. Just says that the heads were replaced with "2 - Merchead" at $1075 each (ouch!). I guess I'm going to have to take a valve cover off to look at the casting number.

I can tell you this...my late model GM replacement engines in my gibson take a long reach tapered seat plug..ran for 2 years with the wring length plugs, had no idea they changed the plug lenth in the heads...now as far as I know only the oval port vortec B/B heads take the long plugs..checked the rect ports heads and they still use the std R43 sytle plugs...

The plugs I pulled are listed to fit either a BBC or Hemi. They use a gasket ring... and are different than what I've seen for the Vortec heads.

When I search this series of plug, they come up fitting AFR, Brodix, Edelbrock, Merlin. Nothing factory related.