With a 'stock 350', I would suggest looking into an Edelbrock Performer dual plane intake combined with a Holly 600cfm vacuum secondary carburator. This combo will offer better low-end torque than a larger set-up would for your stock engine. Stick with smaller and faster intake charges for your set-up. Go with anything larger and you will most definitely punish your car's low- end torque numbers. On the other hand, IF you plan to re-build your 350 in the not-so-distant future, then you may consider investing NOW in the right carb/intake combo for your new re-build.
You will have PLENTY of room on a 71' with a cowl induction hood. On my 70' Malibu, I run a 750 double pumper with a 1" phenolic carb spacer and a 1/2" nitrous plate atop an Edelbrock Performer RPM intake. With a large 14 x 4" K&N air filter, I still have about 1" to spare before the carb stud hits the stock cowl hood underneath. Have fun and enjoy your selection!