Corvairs are the same way--horizontal lifters.  We used to run a pint of
ATF in the oil if the car was used infrequently, as in show car or
convertible, not daily beater.    It seemed to keep them quiet.
Interestingly enough, the Chevrolet manuals also called for 2 turns from
zero lash.  We would adjust the lifters while the car was running, using a
half valve cover.  You back off the rocker nut until it clacks, wait to see
if it will pump up more...  Once you found the quiet point, you tightened
to pre-load.  We all found 2 turns was way too much also!  Most of us run
1/4 or 1/2 turn at the most.  You may get some noise on start-up, but it
quickly goes away.  2 turns would burn your valves in no time.  (They are
air-cooled and do run hot.)   I think in the new motors with new lifters, 2
was OK, but not on a high mileage car.
I am currently running new lifters in my '85 Westy.   I think I will go
back over them and see exactly where they are at right now.  I may want to
back them off some and see if the power increases and whether or not I get
any start-up noise.

                                                                  Jay