they are very similar, Bedford 28hp started off with Chevrolet derived engines in the early days but then developed them themselves and improved the engine is some ways.
some differences are the capacity Bedford is 214 cubic inches where as the Chevrolet is 216.
the Bedford has full pressure oil system the Chevrolet has "dippers" on the big end bearings.
Crank shaft Bearings in the Chevrolet are babbit type bearings and need to be shimmed to the correct clearance, Bedford uses different sized standardized white metal bearing.
i think the Chevrolet has a rear main oil seal (rope) the Bedford does not from memory?
oil line to cylinder head passes through the water jacket on the Chevrolet, it goes directly to the head on the Bedford
The side panel covering the push roads etc on the Bedford engine only goes up the base of cylinder head, the Chevrolet it goes to the top of the head and shrouds the spark plugs.
different water pump, thermostat etc.
there are no doubt many more differences, many people prefer the bedford engine due to its superior oiling system and being easier to rebuild. The Bedford 28hp was developed further after the war and was called the 214, they got a lot more hp out of the essentially the same block.
Hope that helps