I am getting ready to install my rebuilt engine and want to find leaks in the tranny. I replaced the reverse switch [it was leaking for sure] and I am planning to replace the shift shaft seal.

Is there a good way to test for other leaks, say put in tranny oil and let it sit?

If you didn't replace input and output seals you may find out the hard way where the transaxle is leaking. the input seal will soak the clutch with oil. PITA and WALLET to not do this inexpensive job. Speedometer O-ring also. Cheap and easy but will make a mess on the exhaust which will stink to high heaven.

My clutch was dry when I pulled the engine...is it still a good idea to do the seals?I have a new set of output shaft seals...are they an easy install?

PS..were you refering to the mainshaft seal?

Yea Input (main shaft) Whatever make you happy. What does a clutch cost these days. Compared to a 10 dollar seal.

just wanted to be sure

This is a no brainer. If the tranny is out of the car, replace all of the seals.

Your assuming I have one!

no no no. I said a _no brainer_.