I am looking to buy an Offenhauser intake with numbers 6129 and 8-19-5 on it and it looks like thee is no insert with it. Based on your catalog listings it is a Dial-a-Flow intake for Chrysler 340/360. Is this correct? Should there be a threaded hole at the bottom of the intake plenum?
Yes the 6129 is a dial-a-flow intake for a chrysler 340/360.
No there should not be a threaded hole. The flow control insert is held in place by the required adapter plate. #6151. You will also need 2 part # 6151 gaskets. Only the stage 1 (part # 6132) and stage 3 (part # 6134) inserts are currently available.
For more information on our dial-a-flow intakes please refer to a writeup on page 12 (13 in pdf) of our last print catalog which is available here: https://offenhauser.co/wp-content/uploads/2018/04/Offenhauser-Catalog-1987.pdf