I am in the middle of rebuilding my pinto engine and was wondering which size of webers I should go for, the Kent brochure give you rough sizes but I am going for a moderate tune of about 140 150bhp building it balanced and lightened not the crank yet, should i buy 45's or 48's as in the furture i am aiming of fitting nos?

This might give you some ideas:

http://hometown.aol.com/DVAndrews/webers.htm

I certainly wouldnt advise fitting 48's. With your predicted power output you are on the crossover between 40s and 45s. For road use, the car will be far more pleasurable to drive on 40s, and will be easier to set up for part throttle use, where you will spend most of your time. Top end power will only be reduced slightly, if at all.
Also, if fitting Nitrous, carb size is irrelevent as the extra oxegen within the gas that is injected is what gives the extra power, the carbs having no effect at this point.

i would go wit the 40s if its just a mild tune cheaper on petrol easier to drive and easier got and cheaper

and u can always sell them agsain and go 45s if u rebuild to a higher spec