If you're building a fleet of motorized surreys, costs of parts, labor and maintenance would be compounded. Each powerplant would be vehicle-specific.
I got me a BRILLIANT plan!!
Rig up each surrey to accept the same push trailer.
Build all your push trailers EXACTLY the same. No CVT drive necessary, since parade speed is crawling speed. Concentrate on low-end torque and dependability/reliability.
You could have six surreys and four push trailers. If surrey #1 has a last-minute breakdown 30 minutes before the parade, simply unhitch its push trailer and hook it up to another surrey. If the engine or push trailer develops problems an hour before parade time, simply replace the entire push trailer.