First of all, make sure it is operating correctly.
Is there anything to be done internally to improve receiver performance
You are looking at a 35 year old radio - many components (especially capacitors) degrade over time.
If you haven't got the test gear needed or the experience needed to "do it by ear" it's going to be difficult, or expensive(it you pay someone else to do it).
the noise floor on this radio is terrible
They aren't too bad when they are working correctly, you could have a noisy component (capacitor / diode / transistor / resistor) causing your troubles.
changes I could make?
Before doing mods, make sure the original circuit is operating correctly.
Modifying a faulty circuit to increase its performance is like putting a turbocharger on a clapped out 1986 ford that uses more oil than gasoline.
The turbo might
increase performance, true, but you would get better results fixing the original issue that caused the lack of performance in the first place.
It looks like they"general electric" really cheaped out on the 455khz filter!
That's the least
likely component to cause a high noise floor.
The 455khz filter is there to remove adjacent channel interference, not to reduce noise.
Without details such as sensitivity measurements, can't help any more than that.