Probably won't make any difference to the value Martin. Certainly won't increase it, but it may put some potential future buyers off if not original spec...
Then again, it's a Morgan, what's original???

Oh, Welcome to the forum BTW.
Welcome to the forum. All Morgan (and plenty of other) questions answered here.
I am having the same thoughts regarding my 4/4, a CVH, (a) do I go for a bored-out CVH, (b) do I replace with a 2.0lt Zetec etc etc. and have been advised by others and I have come to the conclusion as Graham.
If you intend to keep the Morgan for some time I would suggest the upgrade to ST170, otherwise every time you drive the Morgan you will be thinking "I wonder what it would go like with that bigger engine

"