... make some hard, expensive choices.... or live with .. part....

They will get it as close as they can. The engine was about .4 ips
imbalanced to start with - not so terrible, FAA certified limit is 0.2
ips. Any improvement will certainly help and may bring it within the
0.2 ips. Remember that this engine redlines at 2800rpm compared to an
auto engine at about 6000rpm. The same mass imbalance forces are one
quarter that of an auto engine.

There are some tricks that can be done:
A.) for heavy rods big end - cut off four of the six castle nut crowns
to save almost 2 g or use a longer heavier nut with a slot where the
cotter pin goes to add 2 g to light big ends = a difference of 4 g.
B.) We will also look at matching light pistons with heavy small ends
and heavy pistons with light small end.

My engine is listed as EXPR-OTHER and not as not as a certified
Franklin - required 40 hours test time. This allows using a little
ingenuity to solve such problems.