if it is knocking an it is loud enough you can hear it, dont rebuild it. It would cost more in parts and machine work that its going to cost for a new motor.

The b20A5 wont fit, but you can pick up a B20B from NADAUTO.COM for $700 with a 6 month warranty.

You could find an LS motor cheaper but it will be used and there is no telling what you are going to get.

If its knocking, hate to say it but your going to need a new motor.