Brake servo part number

My 88 defender has had a lot of mods, so not sure if this one is original (doubt it), or if it even needs to be original? But looking to replace it (sheered bolt) and struggling to work out what part number to hunt for.

Parts catalogue gives me options for:

One port
2 port
Type 50 (227 dia non return valve bottom right)
Type 80 (276 dia non return valve at top left)

I have attached a couple photos. Any help appreciated!

I am also considering replacing the servo unit for completeness (pretty cheap!), so i don't need to be restricted by the one i have if that makes any ods.

STC442R or NRC4772.
Better still, why not give John Craddock a bell and ask them?

Looks like mine, the early type. Just measure the diameter, I think it's the larger one - 276mm

yeh its 276mm. and with the port being top left, i think that puts me to a Type 80.

Thanks for the help