I may try to fabricate an under-cabinet range hood, and would use a range-hood insert with integrated baffles and lighting, so fabricating just the "shell".

All of the inserts I've found so far have a top-mounted circular exhaust vent, which wouldn't work in our case without major expensive cabinetry work. Are these inserts also made with a rear-mounted rectangular exhaust vent (approx 4x10)?