those ARE NOT 1968 crank's they are 1967 and previous , the chrome knob's are 1966 and earlier , those are not even close to what 1968 up crank's look like ,
THE 67 plastic knob's were totally different from those chrome one's , they DID NOT put plastic over chrome the 67 plastic knob's are unique to the 1967 model year ,
the parchment knob's are out there but are rare , they pop up on ebay all the time ,
also they are now reproduced and might I say VERY WELL REPRODUCED ! for the 1967 model's ,
but they are not cheap , if you want 5719477 crank's with parchment knob's get your credit card out and here they are $39.99 each ! , but these ARE NOT CORRECT FOR 68 up ,
http://www.ecklers.com/product.asp?pf_id=51999&dept_id=1666#