Nice to hear, a fellow 478 swapper
The 478 is externally balanced, in the front pulley and flywheel. Take a look at my 478 build thread, I am converting my 478 flywheel to work with the light duty bellhousing and clutch.
For the front pulley I'm planning on making a bolt on weight to use the 305 pulley. The 478 4 groove pulley will not work with the light duty timing cover.
Read through my build thread, lots of questions are answered there.