If you did not drain any oil out of the transmission or the converter, then it should be okay to start it up. Then check it warm with the engine running to make sure its at the right level.
Also make sure you get the vacuum line connected up to the TH350 modulator and that you have metal line (not a rubber hose) running up to connect to manifold vacuum on the engine. The short hoses that connect to both ends of the metal vacuum line running from the engine also seem to pop off fairly easily as the hose softens and gets hold. Using a new piece of rubber hose on each end reduces that problem.