BOP 65 and up, 64-67 Buick had one starter hump,
https://4speedconversions-com.3dcartstores.com/581.html
https://4speedconversions-com.3dcartstores.com/bop.html
You can cut the driver side one off and make a cover plate.
Brand new ones here:
https://www.opgi.com/drivetrain/driveshafts-drive-chains-couplers-yokes/1965-72-aluminum-bellhousing/bellhousing-4-speed-1965-77-bop-aluminum-g240720.html
https://www.moderndriveline.com/shop/bell-housings-accessories/bop-bell-housings/bellhousings/bop-aluminum-bellhousing-muncie-t10-gm-tko-patterns/
Good prices. Too bad, no Tremec 6 spee BH. Art.