In a TKO600 I bought last year for another car I was advised to use
Amsoil. I just bought a TKO600 from Std. Transmission & Gear for my SPF and asked JimiG to include the correct fluid with the shipment. They sent 3 quarts of
Amsoil Synthetic Manual Synchromesh Transmission Fluid SAE 5W-30
so there's another option.