FIRST before you waste your money on some whiz-bang alternator it is time to do some basic electrical maintenance.
What you describe is not totally abnormal to begin with. When you hit the brakes, turn on the lights, wipers, heater lighter, etc... there will be a momentary deflection of the ammeter needle. With the engine running 1500 RPM or so, it should correct back within a second or so. If not, you have a conductivity problem (a 35 AMP alternator is more than plenty for your car with original systems.)
As mentioned above, voltage is water pressure, amperage is flow. If your pipes are clogged, it doesn't matter how much water is in the tower, you'll only get just so much out of the faucet! Time to clean the pipes. Good news it this is a super cheap fix (a can of electric contact cleaner, 2 packets of dielectric grease, and some 220 grit sandpaper).
DISCONNECT THE NEGATIVE BATTERY CABLE ANYTIME YOU TOUCH ANY ELECTRICAL COMPONENT!!!!!
Start with your battery cables: Clean the posts and lugs with one of those wire brush cleaners (if you don't have one get one and keep it in your trunk tool box). Get them nice and bright.
Next, clean the other ends of the cables: The NEG attaches to the left cylinder head, the POS attaches to the main binding post on the starter. Brighten all faying surfaces of the connections with sandpaper and wash down with contact cleaner. Reassemble clean and tight.
You have (2) body grounds: One is a 10 AWG wire from the NEG battery cable lug to the radiator support and the other is between the right cylinder head and the firewall. Clean both per the above. If you see any corroded up ghetto-assed crimp connectors on the battery cable to chassis ground, THAT'S probably your problem.
This brings us to the firewall connector. Even if the problem is much better now, and it likely will be, you need to clean this part! There are three connector plugs which can be removed on the engine compartment side. You can generally phenagle them apart with a screwdriver and a little bad language. Clean per the above but pay close attention to the 10AWG wires. These are the "everything wires" or main DC bus. Every single electron from your alternator goes through this connector to the dash, through the ammeter and then to the ignition or headlight switch for load distribution. Those lucky electrons which don't get tasked to run some bulb somewhere go back through the firewall connector and on to charge the battery. Long story short, everything goes through this connector. It WILL melt down if it hasn't already. Clean it and pack with dielectric grease.
Lights come next: Clean each socket and fill with dielectric grease and a new bulb. Don't even think about using steel wool! Headlight buckets have separate ground wires, clean their connections. Rinse, lather, and repeat.
Dashboard fun comes next, check the grounds first.
Long story short, your description sounds like a bad ground well upstream.
