Engine/Transmission (1994 - 1998) transmission Fluid

[DieselNasty]

Since I rebuilding my transmission I have been thinking about the fluid I will use. I used to have regular fluid now I want to go with some Amsoil. If I got the transmission together then drove it and then changed the fluid, to make sure everything is clean inside, could I go from regular to synthetic or would I have to empty the fluid lines, torque converter, and so on? Would it just be easier to start with Amsoil and change it out with the same fluid?