When a stroker kit says that is internal front ballanced and external rear ballance what does that mean

 

It means it's an externally balanced kit. You have both internally and externally balanced version:

Internally Balanced - Zero or neutral balanced at the crank damper and flywheel and it is balanced as an assembly crank rods and pistons.

Externally Balanced - Little balancing was done at the crank level and it is counter balanced normally at the rear flywheel on these cars. The crank hubs are neutral balanced from the factory on Lt1's and counter balanced at the flywheel.

Externally balanced is the way these motors come from the factory but it is known that internally balanced assemblies are the best way to go. If you do go with an internal balanced assembly you will need to zero out your flywheel or flexplate. I had mine zeroed out for about $65 at a local machine shop and they took metal out around it and put it on a balancer until it was zeroed out. At that point you rely soley on the assembly balance to keep things smooth which if done correctly should be within 5 grams all the way through which will lead to prolonged engine and bearing life.

 

Did this help you any?

 

Well stock LT1's are internal balanced at the front and external at the rear so I would guess that means the crank is a drop in for a stock LT1.
I'm having my rotating assembly fully internally balanced and I got a TCI internally balanced LT1 flexplate.