The subject of "matching numbers" is a pet peeve of mine. Yes, it comes from the Corvette world and has, in my opinion, done significant harm to the collector car world. The obsession with it is so extreme that many now apparently consider it an all-or-nothing, make-or-break criterion.
I sold an MGB-GT V8 last year, but initially forgot to tell the seller that the block had recently been changed. I contacted him when I realized that to inform him of that fact before he came to collect the car, and he backed out of the deal. The money was already in my bank account, we were within days of him taking possession of the car, and he backed out. This was a 1974 MGB-GT. Let that sink in. I can understand using matching numbers as a tie-breaker criterion for rare, exotic machinery, but on an MGB-GT?
It's gotten so bad that some, maybe many, collectors will not even touch a non-matching numbers car, as if it renders the car worthless. What a pity for us all.
An engine block is a car part, nothing more and nothing less. Many parts are changed in the life of an old car. There are many numbered and dated parts on a car, Healeys included, and in my opinion the all-or-nothing attitude about them is senseless. It is, however, a reality that we must live with.