Bigted is right, it would be a 1996 model.
Tecumseh has been out of business for many years, ebay is your best bet for replacement carby and potentially a coil, GA spares (available through any good mower shop or ODK site) have a few carby parts and air filters and drive cables.
Many parts are the same as newer 660's. clutch is the same (occasionally weak) and clutch springs readily available.
One thing that isn't is the front double sprocket which is chain driven from the motor and drives the chain to the rear roller.
Older models were left hand thread (hence unscrew clockwise), newer ones are regular thread.
Pretty sure they don't make them anymore - they were hard to get pre covid from memory.
Solid enough mower
Looks like it could do with new rollers at the front. Go to a local mens shed or someone you know who has a lathe and turn up some new ones from a hard wood. Masport don't sell wood ones anymore and the steel replacements are eye-wateringly expensive given how many you need for a 660. Also a good opportunity to increase the diameter of the rollers if you intend on mowing buffalo as the maximum 30mm cut height is slightly low in my opinion for buffalo.
