Most of the spacers listed 4500 manifold to 4150 carb have the holes tapped on the 4500 side and pass through holes on the 4150 side which is the opposite of what I need.
Any idea if the Wilson spacers are this way was well? If not I can call on Monday and ask. edit: Wilson does make a 4150 carb to 4500 manifold adapter...
I have two 4150 to 4500 adapters, one was used on a 4150 intake to mount a 4500 carb., all the holes on one of the adpaters are removed(drill out) so we used bolts to mount the spacer adapter and the carbs The other one still has the threads on the 4500 side I would try these type adpaters and remove the 4 hole divider from your top, the Indy 4500 tops have a open top
The other one still has the threads on the 4500 side 
and remove the 4 hole divider from your top, the Indy 4500 tops have a open top 
