I don't think a horizontal rebar will be necessary.
You may consider the wire mesh they use between the horizontal joints. You only have two block high so it may not be necessary.
Phil Moderator, The Engine Shop, Interiors and Project Journals
1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes Project Journals Stovebolt Gallery Forum