Howdy from the other Schjeldahl brother.
Dave told you about the carb hole in the intake log increasing from 1.5 to 1.75, so your current carb won't fit without making some sort of adapter. Easy enough to do, but why not just upgrade to the later carb too?
If it is there, grab it too.
The 81 will have a cable throttle linkage too. If you can get the gas pedall and cable too.
So let's see. You're getting a bigger log, bigger valves, hardened valve seats, bigger carb, electronic ignition, cable throttle, ALL FOR FREE! Hmmm... there's going to be some jealous people around here. The only down side is the loss of compression - so mill the crap out of it, backcut the valves, and be happy.
Go read the "head swap" sticky on the small six thread and the "What a three angle valve job is" on the hardcore inline tech thread.