| Have the heads got a letter stamped on them to the left of the plug hole and up a bit. The 600SS's have the letter K
If the plug threads had stripped then rather than get them helicoiled they could have taken them out to the next size replacing the standard DP8EA plugs with BP7s
As Antony says the Engine number on the left side of the engine below the alternator should indicate what engine size it is.
If its originally a parrallel import then they did have 33bhp versions in France and other countries, also people in this country did get 33bhp restrictor kits fitted.
Best to work out what you do have first Chad
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