The bolts for holding the intake to the head are 5/16”x18 and are 2 1/4” long, but they have captured washers taking up a tiny bit of that length.
The FelPro ES 72169 mentioned above is correct for factory style replacements that are fully threaded. The original bolts are often badly rusted in the front and rear positions on both heads, which is why the replacement sets are available.
Cheaper hardware store grade five bolts can be used, but make sure they don’t have a long shoulder that can bottom into the threads.
Finally, Edelbrock aluminum heads have blind holes and factory style bolts bottomed out on mine and needed extra washers. Factory cast iron heads don’t have this problem.