I would absoutley have this (or any other engine that is being built from seperate pieces) balanced.

The balancing procedure is used to eliminate vibration in the engine that frees up HP and also helps ensure engine longevity.

The balancing procedure consists of 2 parts.

Static: This consists of; measuring and equalizing the weights between pistons & Pins, Rod small ends, and Rod Big ends.

Dynamic: Which consists of spinning the crankshaft with the balancer, flywheel/flexplate and "bob weights" (it may also include the torque converter/clutch cover)

The catch is to balance the crank properly it must be weighted on the crankshaft journals (bob weights) to simulate the weight of the componets that are attached to it. The formula is 100% of the rotating assembly weight (rod big ends to include rod bearings and rod bolts) and 50% of the reciprocating assembly weight (rod small ends, pistons, piston pins ((and keeper if so equipted)) and rings).

If the bob weights that are attached to the crank are not exactly the same as what the engine will see in real life it will not be truely balanced.

Chances are your crank is "balanced" to an abritary figure (likely factory weights). The rods you are going to use may be balanced to each other (total weight) but may not have that the small and big ends equalized. Same holds true for pistons, many replacements are balanced sets however those weights are unknown to the crank manufacture,for instance Forged pistons generally weight siginificantly more thatn cast pistons.

Most engines can live with a certain amount of imbalance and not greatly affect them. A good example is an engine that is bored and new pistons installed, in many cases the engine is no longer at the same balance but the change is not siginificant enough to be noticed. The same holds true with using a replacement balancer,or flexplate/flywheel, the difference in balance on the replacement will likley be too little to notice. At a certain point however if it is too much out, the engine will literally shake itself apart.

When you are building an engine from separate componets (especially aftermarket parts from different manufactures) the chances for much greater for being siginificantly out of balance. If thats the case the engine will need to come back out, torn all the way down, balanced and then reassembled. In my mind that is more cost and a lot more aggravation than having it done before the engine goes together.

Hope this helps.

The only thing you shouldn't need for the balancing is the main bearing set.