When I got my Grandpa's 1951 3100, I discovered that the battery hold down was AWOL. He had a 1" wide canvas belt strap and spring clip securing the battery to the bottom tray. One of my brothers who builds industrial metal working saws fabricated and welded up a copy cat hold down bracket that ended up having the same problem you report of contacting the battery posts.

My solution was to notch a semi-circle cutout of the angle steel flat top area at each post location to create the gap needed to prevent direct contact. The hold down remains plenty rigid and I also added a glued on flat rubber strip on the horizontal underside of the bracket so the metal hold down wouldn't damage the battery case through direct contact.

~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)