2-liter radiator cap

[Arthur Rockwell <arthurrockwell@sbcglobal.net>]

I put a 2 liter radiator in my 96% complete '66 SPL311 SR20DET, but I cannot 
find a radiator cap!!!!  We have tried a number of different caps and none of 
them fit right:
 
1) does anyone have a source for the correct cap?
2) does anyone have a new/used cap I can buy?
 
Thanks.
 
Arthur Rockwell
'66 SPL311 SR20DET
North Hollywood, CA