There never was a hood liner on Amazons but you could put one on.

Have your valve lash, timing and carb(s) checked for proper operation, and have the exhaust gone over for leaks.

Good insulation on the inside of the firewall helps.

If you have the original B18 motor with stock diameter exhaust and all of the tune-up stuff checks out, I can't imagine it would be very loud at all.
When I had this configuration on my car, I would think it died at every red light.
Best,
shayne