Gearing up for a swap on my 68

[Accelo]

If you want to move the motor forward enough to retain the stock driveline you will be reducing the clearance between the motor and radiator by roughly 2.5" While this may be fine depending on the fan configuration it will look silly with the motor that far forward.
This is assuming you are changing out the transmission for a 4L60E. If you are retaining the stock transmission it should work fine as the motor mounts are typically designed to put the motor in the stock location. Adapting a LS to a early SBC transmission requires some research to get the correct flex plate.