thumpr is a big cam even the smallest one is pretty big for a 305. They are made to make 350 motors lump around so for 305 they can be a bit much.
compression ratio is a big deal with larger cams. If you have a cam that is too large with low cr it will not perform.
Th700R4 is a better choice unless you really want to spend the bucks. You can buy then built nd complete for 700 bucks ready to drop in the car with shift kits and all the toys. a proper built 200r4 that will take 300 abusive hp is alot more cash. You do get something for your trade as it is smaller lighter and uses less power to turn it over. But a proper built 200r4 can cost 1500 2 grand for something you can depended on. 700r4 can be rebuilt with strong parts for that kind of money.