> Best thing to do is measure the outside diameter of the drain outlet to
> determine which cap it is.  The larger earlier one is 34mm I believe.
hmm i have an 85
the dia from the ide thread to thread is 30mm
the inside dia of the cap (where the hole is) is 35mm
ouside dia  edge to edge 40mm

I think the best option has got to be to get some large die 1.25" say
that is sae thread & chase those threads down

hee a dis for 1 use on plastic cant be more than $5 and as you say 98 cent
cap

any one done that with what exact die & what cap did you then get