Wouldnt agree, thats too big for the big cam your talking about, Id err for something smaller, in my experience a big single carb on the 250-2v with a big cam is very soggy down low, and since your talking about a slushy trans Id be keeping as much low down torque as I could.
The idea you have is fundamentally wrong, a 250 isnt a big rever and as such your better off trying for increased torque, the 2v head will move your torque peak up about 500 -750 rpm and increase it quite a bit, but you wont get peak power much above 5000rpm even with a big cam, so keep your cam under 220 degrees (even thats probably too big) run a smallish carb and since Im assuming youll use the stock 2V intake manifold a smaller two barrel should work well .
So overall where looking at a cam around 215 (25-65) and exhaust port work, the inlets are almost too big stock, a bigger inlet valve will help a little, a good set of headers with a divided centre exhaust port, something around 350-500 cfm carby, 350 is very streetable, 500 gets a bit wobbly with the cam, is OK with stock cams.
This will give a you a good solid torquey thing which will work well with a stock type auto box. I hate loose comvertors and would say they are only suitable for drag racing, far to wastefull on the street.
If this is in a light car, say under 1200kg it will go rewally well and not too heavy on fuel.
All the best
A7M