later further down i want to do b18v or b20v, i was wondering if i switch motors for now then do b18v/b20v later, can i use the same wire harness, and ecu a b16a obd0 uses?

 

Yes.

 

so its all good? just like that.

 

As long as you keep the same distributor, then yes it's that easy. The other option is to convert to OBD-1. Then you would need a Distributor, 4-wire O2 sensor, OBD-1 ECU, and then convert the plugs to work with the new stuff.

 

k well i still have the same distributor, so im going to keep my distributor from my b16a so that i could have to get all that stuff.