You can in the motor or primary but that is way too thin for the protection of the transmission.
My suggestion and what I like to use,
Syn 20w50 in the engine.Like mobil 1 etc.
Reg 20w50,primary... Change it often so it gets the friction dust out and I dont like to use synthetic here as it can cause clutch slippage.
Syn75w140 or 75w150 in the trans... Change it often so the bearings can live.