Well, I could possibly start the ball rolling here with my experiences with these two engines, not in Morgans though, in Caterhams.
First of all welcome to TM, you may find Morgans a little disappointing after your Seven, certainly in the ride, roadholding and acceleration.
I have owned a 2.3 260bhp CSR for the last 7 years, and having sold it last year, I now own a 2.3 200 bhp CSR, and have also had experience with a modified 170bhp black top Raceline Zetec in a Caterham.
I would suggest forgetting the Zetec, it is old technology and heavy too, unless the cost of a Zetec 4/4 is so good as to make it worthwhile. The 2.3 Duratec is now discontinued, and the 2.5 a little difficult to buy, although I daresay they are available as crated engines. This leaves the 2 litre, but to get some real power, you will need to have a decent budget, and plan to keep the car for a long time to get your moneys' worth from it, because I doubt you will sell it in the future for anything like what it will have cost to develop.
I expect you have costed the bits and pieces to tune an engine? They are expensive, and you have to be pretty dedicated to go down that route, attractive as the finished article is, but if you want to do it, I would suggest using a supercharged version of the 2 litre, like the new [ish] R600 uses. Have a look at the Omex website for an idea of costs and figures. I seem to recall they are talking good torque and around 300bhp.
I currently own a Three wheeler, and really, really, want to like the 4 wheeler, but after 25 years of various Caterhams I just can't get my head around the lack of development of the trad. range of cars. I would love to find a Morgan that is light, lithe and fun to drive, in a way that a Seven is. Those who have owned lightweight cars will know exactly what I mean. Maybe though, at 68 I'm just not old enough for a Morgan 4 wheeler yet!
I'm sure this topic will throw up some interesting snippets though.
