I used a universal cab heater from Summit Racing, they are offered in several sizes and configurations. I went with their 40,000 btu/ 300 CFM unit, it moves more at low speed than the stocker did on high, and quieter too. In Minnesota a good heater/defroster is a necessity. I made a plate for the front that has vents for floor heat and provisions for connecting the defrost duct hose.
https://www.summitracing.com/parts/sum-991106/overview/