go into any decent tuning shop and get a little facet fuel pump and an adjustable dial pressure regulator. you should walk away no more than $150 lighter
it's said that with dual sidedrafts, you can see the fuel gauge going down :P maybe on a rotary, but i wouldn't be expecting any better than 8L/100km at least. christ, even a downdraft weber can be worse than that if you want it to be
i'm going out on a limb here - forget sidedrafts. i had a pair of dellortos, and i found them too expensive to bother with, so i gave them to rob, who spent $550 (?) reconditioning them. sure it's going to be a bit more expensive if you buy new carbs and new manifold, if you look for long enough you'll find some which require not much work, and a second hand manifold (i bought my twin sidedraft manifold for $120). you sound like you don't want to spend a heap of money but still want a decent setup with as little compromises as possible. like me :D
learning about SUs the last couple of weeks, and having mine partially apart, made me think how the most simple solution (one needle, one jet, one adjustment nut) is often the best. i would go as far as to say the last 100 years of people fartassing around with venturii and air jets and emulsion tubes was a complete and utter waste of time and effort. george skinner had it right back in 1905 with the SU carb. with a downdraft/sidedraft you tune the car in using jets and tubes until you find two ideal points which your car lies between. an SU is totally "analog" in its tuning, you adjust the thickness of the needle to suit the car, so you can potentially obtain a near-perfect tune, moreso than you can with a carb that uses e-tubes
i reckon, if you can find a pair of SUs on the cheap, you could buy a new manifold and still have them tuned and on the car for as much, or less, than a single dcoe
your workshop sound like idiots, they run a car at ideal power AFR on its run in, then tune it back to stoich after it's run in. most workshops run a WAY rich run-in tune, and if an engine's pretty off its tits (like yours is) run it slightly rich on its' final tune. i've never seen a rich engine glaze rings, and i've seen a few built and tuned. mine runs rich as all buggery, and i've had the head off and the bores are spot on