I think the fuel pump boss can be opened up at the machine shop. Some blocks were drilled for the mech fuel pump.
What are your goals for the car? Nice cruiser, drag car, little of both? I say build the 383. I have been gathering parts for my 383 vortech. Its easier to change heads later on for more power, than to pull the motor back out to stroke it. My opinion is different than turbo78's. A 350 and a 383 set up with the exact same, the 383 will walk all over the 350 and be a milder motor. If you get the right crank and rods, there might not be any clearanceing needed on the oil pan rails. Get a 1pcs rear main stroker crank( eagle, scat, etc.) and a good set of rods and pistons.
Turbo mentioned sacrificing rpm. You can build any motor to turn whatever rpm you want but durability becomes an issue. If its a race car it may see high rpm for a few seconds during a race. If your car is a street car or a little of both, most of your rpm is around 2000-4500 rpm depending on transmission. I'll take the torque down low where i can use it instead of a bigger hp number at an rpm that isnt used.