It's going to be somewhat expensive, no matter which route you go.
Probably your best bet is a good used Edelbrock aluminum , or original cast iron intake, both very easily available at swap meets and e-bay .
Most expensive route would be the Edelbrock STR 14 with 3 x 2 top plate .
As far as the Offenhauser, the only ones I am familiar with are set up for
either strombergs or webbers ?

Greg