You have other options. Cylinder sleeves, with the stock bore are available for you car. TRF lists them in their parts database. $35 ea. They also list a bare block, short blocks, whole engines. Give them a call.
But then, there is the concern about the head, I would also wonder about the crank, cam,....I got a headache.
What a nightmare. My sympathy.
Oh, I remember there once was a place near you that restored TR's and was a Moss distribitor. Can't recall the name or if they are still in business, but they had a lot of parts cars....
Good luck