Changing Automatic Transmission for Manual one

Hi there!
Despite of all other challenges when doing so:
Does a manual transmission fit into a 1991 K10 (with 1,2 Litre 40kW and automatic transmission) without major changes on motorbloc ect.?
If so, which manual transmission exactly do I need?
If not, what would be the necessary changes to make the manual gearbox fit my K10?