I believe manual and auto engines are ballanced differently,  is changinf the flywheel to a flex plate going to change the ballance?

Having done a 1.6 swap in my Samurai and removed/reinstalled a 1.6 on an automatic Sidekick, I don't think that you can even put a flywheel in the place of a flexplate.

First there is the matter of flexplate thickness (thin stamped steel with a gear welded to it's circumference) vs flywheel thickness (machined, thick, heavy casting with a gear pressed onto it's circumference).

Then there is the way the flexplate is connected to the torque converter which would take a bit of precision machining to accomplish.

Since the torque converter takes up some of the duties of a flywheel (a spinning mass) it seems a bit illogical to put a flexplate in place of a flywheel -- not to mention the fact that the flywheel is part of the clutch system and there is practically nothing physically there for a clutch to operate against in a flexplate.

Out of curiousity, what are you trying to do?

change manual to automatic.

but some of the flyweight 's weight is compensated by the torque converter, is it not?

I believe manual and auto engines are ballanced differently,  is changinf the flywheel to a flex plate going to change the ballance?

No, if you are changing from and auto to a stick or the other way around it will not be a problem with balance of the motor.

change manual to automatic.

but some of the flyweight 's weight is compensated by the torque converter, is it not?

Yup!

It's pretty much a straightforward swap.  Depending on the year of the two trucks (the key is to try not to bridge between 1995 and 1996 'cause that's the big change year.), The ECMs should be compatible although I'm no expert at that.

You just bolt the flexplate onto the end of the crank then slip the engine in place.

I did all the engine removal/installation with the transmission in the vehicle.  It might be easier (in one way...) to put the engine and transmission together outside of the truck.  There are several braces that bolt between the engine and transmission (at least for the 4-speed I worked with and I suspect they are there on a 3-speed, too) and it might be easier to deal with them that way.

You'll also need the radiator with the transmission cooling core and associated plumbing.

Remember to take a good look at how everything is connected together on the donor truck.  Take pics and lots of notes!

If you can, get your hands on a GM or Suzuki FSM for the donor truck.  Lots of useful info in there!  Especially about the two types of automatics.  I had access to a  '96 GM FSM that proved very helpful!

Finally, replace the input seal on the automatic as they tend to get buggered up.  12-15 bucks is a good investment!

Good luck!

Make sure to get the flex plate and trans from
the same trucklet, 3 speed and 4 speed plates
are different, I don't know if the splines in the
TC are the same or not, but to be safe get that too

There is a small spacer that has to go with the flex plate.  I is on the end of the crank to space the flex plate back.  If you don't use it , your starter will destroy its self the first time you try to fire it up.

Guess how I know this.........