I added a Arca Swiss ball head to my Bog Deathgrip. I also put a riser in because I wanted it to be taller in some situations. The Arca mount will also accept Picatinny rails.
I used these 1 3/16 OD 3/8 ID inside the tripod for spacers to fill the void.
4PCS Multi Purpose Rubber Spacer 1 3/16 Inch OD x 3/8 Inch ID x 1 3/16 Inch Thickness Rubber Bushing Anti Vibration Spacer Black Round Neoprene Rubber Washers for Home and Car Accessories (4) https://a.co/d/cTw1guk
This is the Ball Head Low Profile Tripod Ball Head-INNOREL Panoramic CNC Metal Camera Tripod Ballhead with 1/4" Arca Swiss Quick Release Plate Aluminum Alloy head for Tripods,Monopod,DSLR,Camcorder,Max Load 55lb/25kg (G44) https://a.co/d/as8HNrx
These are spacers to fill the void. The rest are just a 3/8 bolt of your choice and a few washers. I had the plastic part in the tool drawer, I think it came from Lowe's.
4PCS Multi Purpose Rubber Spacer 1 3/16 Inch OD x 3/8 Inch ID x 1 3/16 Inch Thickness Rubber Bushing Anti Vibration Spacer Black Round Neoprene Rubber Washers for Home and Car Accessories (4) https://a.co/d/d8vcZIW