Sparkplugs and head ID

i posted something in the 5.0 tech and got zero input, so i'm posting here. currently on my '66 coupe, i have a matching set of mystery heads. the date code is early '87 or '77? (7A29), but an autolite 25 series plug is way too short (by a 1/2" or so to screw into the hole. the current plugs are autolite 5144 and i would like to replace them because i am getting some off-idle stall. per autolite's website, the 5144 never was used in a V8 and in the 80's it only went into a ford escort.

anyone have any idea what head i have and what plug is supposed to be in that hole? the previous owner claimed the engine is a matched set and the block is for a manual transmission.

my crap-tastic combo is these heads with early 90's stock GT cam, duraspark, triY's, and carburetor (570cfm 4150 on an E-RPM).

i can guarantee you that any help will be greatly appreciated!

D.Hearne said:

I'll bet you've got E6SE heads. These use the same plugs as the GT40P's, but with the std plug angle. Look at the lower front corner of the pasenger side head, next to the valve cover. If that's what they are, you'll find a large "S" cast there. And the same letter on the driver's side head in the opposite (rear) corner.

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yes, they do. so what are these heads good for and what plugs?

Edit: nevermind, i used the search and the results were not that glamorous