Welcome to CHR:
Your comment leads me to believe that you have a two-barrel, stock 350. If it is a 1971, the good news is that it is an L65, which is not a bad little motor. In 1971, this engine was a base for a lot of GM products and typically came with 1.94/1.50 heads and 8.5:1 compression generating 245 horsepower. It was in 1973 that the L65 became the weakest 350 of all time, generating 145 hp at 4,000 rpm and 255 lb-ft at 2,400 rpm.
As it sets, 2x4 would be a disaster for several reasons however; you could do the following and have a pretty nice low-budget build that would get you 300 horsepower.
1. Buy a set of Vortec heads, +/- $500 on eBay
2. Buy a used Vortec intake manifold +/- $150
3. Buy a rebuilt Q-Jet - +/- $225
4. Set of headers to fit your rig
5. Gaskets
This is all bolt on and go and you’ll not get too far afield as this is all stock stuff that will complement this engine. If you want to go deeper and spend more money, you could replace the camshaft and lifters, but this will certainly give you a solid dependable engine that fires right up every time and give you a decent increase performance without much of a sacrifice in mileage

Again, welcome to CHR!
Glenn