I just checked the hinge mount bracket bolts and they are 1/4-28 (NF).

The trunk locking pivot bolt with allen head on the body side is 1/4-20 (NC).

The upper pivot bracket mount bolts - with slotted heads are probably 1/4-20, but could be 5/16-18 (NC).

Four year old 30-31 Brookville body fwiw.