Use either, take the stock cam and throw it away if using the 305. A simple cam change with the 305 will get you the same power as a stock 350. However a simple cam change in the 350 will get you a little more power.
Since both are Generation 1 SBC's parts are equally plentiful for both. differing only in strokes. The ultimate SBC for trucks are a 383 (350 with 400 crank)this combination is cheap, and extremely torquey.
I ran a 305 in a mid 80's Camaro with stock TPI injection with a simple $80 cam change, and added about 40Hp / 35lb-ft torque. Netted a better feel when driving, and also got better mileage. The 305's were built by the accounting department, so they got 2 barrel carbs and crappy cams in attempt to provide low $ V8 power.
Bigmacdaddy - The mid-70's 305's had cam lobes that were almost round (no appreciable lift at all - this was worse when the cams were soft and ate themselves)
