if it was my cab , i'd use a router and clamp on a straight edge and then use a bearing guided cutter to cut back to the required 3/4 inches. obviously , you cant cut a straight line up to the cab sides as the body of the router will stop it, so i'd get as close as i could with the router and then use a bosch all rounder , to cut the remaining waste.
it may not give you a completely 100% straight cut , but it'd be close.
or ,
if your good with your hands, the bosch tool could be used for the full length of the cut.