I am in the same position in that I have a 305 in my 82GMC. Thses are the things that I have done that worked great with out breaking the bank. I call them my under 200 dollars each mods. Ecapt for the intake and Carb.
First I replaced the intake with a Wieand Stealth dual plane and Holley 600cfm vaccum secondarys.
Accel HEI. I latter added the MSD 6al locked out the Distibutor and put in the MSD Timing computor with 4 degree retard at 2500rpm.
Next a catco cat and then a Flow master mufller. I made my own exausht pipes going staight out the back. I did make my own y pie to go from a 1-2 tail pipes it is a delta shape with an internal expansion chamber then it feeds into my 2.5 inch pipes works real good for scavanging.
A home made ram air set up 15.00 dollars in parts.
These mods have really made a big difference in both the performance and gas milage. My buddy has an 80 model chevy pickup his is the standard bed mine the long bed he has a 350 . I can blow him a way going down the road he avreages 12mpg I average 17 mpg
What I am trying to say is dont blow a large chunk of cash but allso you do have a lot of potential. Allso all these mods will bolt to a 350 if you ever get one.