You should probably look for a spark plug if it doesnt have one..
Here in So-Cal.
Twins are .7-.8mm.
The proper spark plug gap for a 1980 Chevy 350 Pickup is .045, according to spark plug manufacturer (Autolite, Bosch, NGK) specs.
You can look up application specific information at every auto parts website such as rockauto.com. autozone.com, or advanceautoparts.com.
.024 to .028
.030
Look at the starter or the spark plug
.044 inch
35
.045 inch.
0.35 gap
.032" good luck