Belt drive and Chain drive.
Like the iconic British 'Mini' car - There's a lot going on in a small space under the S80, 82 & 92.
You have a drive belt with spring, rod and clutch idler - to a Peerless straight-cut-gear box - to a chain case - to an axle-mounted differential unit - to the rear drive wheels.
Plenty of possible failure points and a headache for the technician to unravel.
Most common is belt, idler & spring/rod as you would expect. But a 'Bump' could have caused chain failure in the (now) old drive-train.
No 'disconnect' as such, Motownbrowne. It is a manual shift gearbox with a "Neutral' position between First and Reverse.
If you are not familiar with the drive mechanism take great care when dismantling. Your camera is your friend here. Photograph the belt guides and springs, rods, split-pins etc. Especially the guides as you can set them too close and too far away from the sheave on the engine. Too close and they rub. Too far away and the belt can drop off.
First job will be to get the mower deck 'off'...
Good luck. :horseshoe: