You don't say whether you're going to hang the prop off the nose of the
crankshaft or off the stronger flywheel end of the engine, but either
way the thrust bearing must take thrust loads directed toward the nose
of the airplane. If it's not obvious from the construction of the
bearing which orientation is needed, ask the supplier; some special
prop-hub bearings and housings may not be reversible, in which case
you're up the creek unless you buy a different bearing or even a whole
different hub system. In any case the crankshaft end-play shims need
to be on the proper side: between the flywheel and the #1 main bearing
if the thrust is from the flywheel end toward the pulley end (just as
when rebuilding the VW engine for a car) or on the other side if the
thrust is in the other direction.

You really should talk to a professional engine builder in any case;
one should be perfectly willing to exchange an email or two or take a
short phone call from you at no charge.