My 88 305 would barely turn over so I replaced the battery. After I installed the new battery it will turn over and start but if I kill it right then and try again it barely turns over and may not start. Could it be the starter. It does always try to turn over not just a clicking noise.

 

Verify batt cable and ground connections. If they are good, it's most likely the starter solenoid. You can try replacing that, or just replace starter (which usually comes with a new solenoid).

If you plan on keeping the car for a long time, might wanna consider a gear reduction starter. They work a lot better and last a lot longer. Especially on modified engs.