No thay are not even close.
yes the 4.3L vortech has the same motor mounts as the 350
small block and big block motor mounts are the same, so you should be able to take V8 motor mounts from most any Chevy engine bay.
If the Buick 305 is really a Chevy 305, then the motor mounts will interchange with a Chevy 350.
yes
yes.
NO, They are made different.
No. They are different
NO. Not even close.
YES they are the same engines.
No not even close. Chevy redesigned them in late 1999.
YES.
if it is the same motor yes, but some may have different mounts or wiring plugs