With your 81 you already have the tallest 4th gear that vw ever put in a air cooled tranny, and I figure you have discovered that even dropping into 4th at 60mph it still leaves much to be desired oon the pick up end.   

I personally feel that the acceleration on 3rd is great, and if you made the gear taller, you would lose this acceleration in 3rd gear, but shift into 4th later thus making 4th acceleration better.   

Go with the stock rebuild IMHO.