Early 1100S / Austin 1300 / Spridget etc. Thin flange 1275cc. Restamped so they didn't need to go through an inspection and fit disc brakes.
Price is a different thing as the price is all over the place. Just 2 weeks ago there were some MK2 Cooper S blocks with heads and crank and rods that sold for $900 and $1000. There are some MK1 Cooper S blocks on Ebay now for $500 and $600. The one closest to your engine is one from an 1100S and it is $300.
https://www.ebay.com.au/itm/LEYLAND-MIN ... SwTEJaPH17I would suggest watching the market and see what is a reasonable price that you are happy with.