Hi John . . .

Have you checked out Vintage Speed?

They have all kinds of different linkages to choose from including this progressive setup for Rochesters:
[img]http://www.parts123.com/parts123/yb.dll?parta~showpic~0000106a~99494~~~[/img]

and they also stock the generic Offy one:
[img]http://www.parts123.com/parts123/yb.dll?parta~showpic~0000106a~99431~~~[/img]

regards,
stock49

[Linked Image from 49fastback.com]