With some tinkering, you can put just about any Kawasaki or Kohler air-cooled vertical-shaft engine with a 1" diameter by 3-5/32" length crankshaft. You will pay a premium for a Wright-spec engine, if you can find one, while you may find a deal on an odd-spec engine.
Beware that the 675 cc Kawasakis (19-25 hp FH6xxV and FH721V series) use a different exhaust manifold and muffler than the 17 hp FH541V.
I replaced a 17 Kawasaki on my 52" large-frame Stander (pre 2010) with a CV730 25 hp Kohler about 3 years ago. You need a special muffler and manifold for a Stander (Koher has an accessory catalog for part numbers), but the exhaust is cheaper than the Kawasaki. Some rewiring is required (a longer ground, the starter solenoid is on the starter on the kohler while remote on the Kaw, and the carb solenoid wiring is a bit different) and you need a longer fuel line.
I used a Koher with the "commercial mower" air cleaner (high mounted round cleaner) with top throttle and choke controls, a metal "chopper" grill on top, and a premium oil cooler. It had a 4" long crank that I chopped down. Kohler commands vary greatly in quality; the ones with the air filter mounted low, a plastic grill on top, and plastic intake manifold are much cheaper (you can get them for about $600 on occasion for a 25 hp).
The only problem I've had with the Kohler is it tends to backfire if not shut down a high throttle (something my older 22 hp Kohler didn't do), which blow out mufflers and head gaskets if you aren't careful. Otherwise it is powerful and gets good fuel economy.