I assume you are measuring the front cover height (block height) bottom to top, oil pan face to cylinder head face?I measured my 1600 which has the spin on adapter and my 1750 heights. Both are 280 mm.
So as not to lead others astray, Can you go and edit your post above if you made some mistake in measurement or in undersanding what parts you were measuring. For example if you measure two 1600 covers and not one 1600 and one 1750.So I must have a late model 1600 front cover on my early block.?
I was offered the part when I was gathering the bits together for my Sprint GTV engine. Coming from Austin Healeys was happy to offload the canister oil changes !