I just had to deal with the same. The 235 manifold I found here on the site had a 1/2" solid plug, and I am far away from proper parts. I found a short section of former steel gas line, bent 90 degrees. I drilled a hole in the center of my 1/2" plug and glued in the gas line with JB Weld. Then rubber line to the wipers. It works so far.
Karl

It may not be the easy way, but it is the Cowboy Way - Ranger Doug
Beware of the stories you read or tell; subtly, at night, beneath the waters of consciousness, they are altering your world. - Ben Okri
1953 Chevy 3100
1960 Volvo PV 544
1941 Chevrolet Special Deluxe