I have a '93 Buick Roadmaster, it came equipped with a Chevy 350 TBI (not an LT1) and a 700R4 or maybe a 4L60. I am gonna swap the engine into my truck with a Muncie SM465 tranny. I want to have all my conversion parts ready before I pull the engine from the Buick, and therefore need to know some stuff.
(1) Is it a one-piece rear main seal? (I am pretty sure it is.)
(2) Do I need a 168 or 153 tooth flywheel?
(3) Is it internally or externally balanced? ( I thought only 400 small blocks were external, but maybe later 350's were too?)

 

350,s are all intern Bal.
You might have to change the oil panand pick up
In 1986, GM changed their gasket design to a one piece rear main seal. The earlier style oil pans will not fit the newer blocks. The computer controlled blocks in the '90s added oil level sensors
The flywheel can either be 153 tooth, measuring 12-3/4 in diameter, or 168 tooth, measuring 14 in diameter. Depending if you have a small or large clutch set up The 1985 & earlier flywheels are not interchangeable with the 1986 & later flywheels, due to a change on the flywheel crank bolt pattern and balancing. If you are using a stock GM bellhousing, make sure you have proper clearance for the flywheel. For the proper starter, GM used two different bolt patterns on the bottom of the block. The straight bolt pattern is normally used with the 153T flywheel, and the offset or staggered starter bolt pattern is normally used with the 168T flywheel.