Looks to me to be around a 1970 model Mayfair.
Originally it had a fishtail-type exhaust but someone has cut a slot in the alloy base to fit a post-1972 type muffler.
As vintmow has suggested buying secondhand parts on eBay to replace the missing components will cost a small fortune. New parts are largely no longer available; you can get blades, blade bolt and nut sets, air filters and decals, all as reproduction parts. You’d probably be best to keep an eye out for another mower or two, either the same or very similar and to make one good one out of two or three scrap ones.
Sources to look out for them at are: tips, hard rubbish collection days, garage sales and markets. The going rate for a non-runner that may be beaten up but complete varies anywhere between $50-$150 depending upon the place it’s being sold, the model and condition. Catchers in decent usable nick are very hard to get for these “low arch” models or any mower from this era and can fetch very high prices.
