? on 7 1/4 to 8 3/4 rear end

Ah DUH,,, sorry about that, it has the stock 904 automatic transmission in it and I am using that. The engine builder is getting me the torque convertor and flex plate as the motor is going to be dyno tuned before I get it. Will I still need that spacer ring or should the builder know this? and where can I get it if so? Thanks!