@aa335,
Do you know whether the Toro 621/421 can accept Honda GX160 engine? Do you know whether the engine on your Toro uses standard 3/4" shaft? Thanks for your help.
Can't say for sure, haven't poked around inside the machine getting measurements.
The current engine is probably a GX160 clone so everything is likely to be similar in dimensions; the power is going to be the same too, or close to it. No point to do the engine swap unless it fails or it gives you comfort having a real GX160.
Honda has updated some of their snowblower models this year, hopefully, there's going to be a HS520 update or redesign sometime this decade
. Hopefully a GX200 or GX240 finds it way in there, in the form of a HS621. Just hoping....