Welcome Charlie to this forum and to +8 ownership in particular.
I am thinking about your car and its history but nothing comes to mind immediately, but there are some interesting facts.
One can never be sure about time lines with Morgans but I think that a 1990 car would be a 13CUX or "Flapper" fuel injection or possibly even 14CUX (Hotwire) as 1990 was the change year. To convert a car from fuel injection back to carbs is quite an undertaking, so if this is the case it was obviously not done without very good reason. I think it is also important to establish what other mods have been done to the engine esp the camshaft.
The quad downdraught carb set up , be they Webers or Dell Ortos, was not an uncommon modification in the competition sphere, but much less so on a road car.
Certainly most cars with 14CUX (or "Hotwire") were given a fuelling chip which gave a very satisfactory performance for general use, and only someone wanting to compete with it would need more.
I know at at 2 cars that were so converted by I & J Macdonald (the NE Morgan agent) from 14CUX to quad Del Ortos, but I think they both fell fowl of the emissions test once this became more stringent.
Thinking about fuel consumption, how much better than 19mpg are you hoping to achieve? I would say that 20 mpg when the car is driven hard is pretty good and it would be difficult to achieve better with carbs (whatever they are) . Just to give you an example my 14CUX 3.9 injected engine (with mild John Eales tune) gives 26 to 28 mpg when cruising at up to 3000 rpm , but it quickly falls to 23 to 25 once I up the revs to 4000. If I start to use high revs and low gears then low 20s is the best achievable and that is with the more economic system of injection. It is going to be worse with carbs I fear whatever you choose.
Side pipes are an acquired taste. For competition almost essential (you want to hear your own motor) but for touring they can be wearing on the ears, esp on long journeys. I prefer to go with long pipes out to the rear and no resonators. That gives a nice burble , but I have cats on my 1999 car, so your exhausts are going to be louder whatever you do. However many prefer the "crackle" that emanates from side pipes on lift-off.
