I know it's going to be expensive, isn't everything racing related expensive? I plan on spending about $3000 for this build, I think that should get me a few more ponies. As for the bottom end, will your Carrillo steel rods work in the twins? If not, here is the machined billet performance rods that Hitchcocks provides for the twins.
http://www.hitchcocksmotorcycles.com/news/25099/New_Twin_Conrods_Available
Scottie
I doubt that the Bullet 500 Carrillo rods will fit in the twin, but there might be some steel rod that will work for it.
The issue with aluminum rods is the fatigue life. They eventually give out, no matter what kind of aluminum rods they are. How long they last is determined by the amount of stretch they get when run hard, and after a certain number of stretches, they break. If they are run easy, they will last thousands of miles. If they are run hard, they might only last a few hundred miles, and you never really know exactly when they are going to break. Top-fuel dragsters change out their aluminum rods after every event, or sometimes after every run.
I'd recommend steel rods if you are going to run them hard at the drags and don't plan to change them out each year.
The weight difference isn't as much as you might think. A Bullet OEM aluminum rod only weighs 100 grams less than the Carrillo steel rod, and the reciprocating end weight is the same. The 100 gram difference is on the big end which is easy to compensate in balancing, and there is no reciprocating weight increase to add stress to the crank in reciprocating motion. And steel has no fatigue life, so it won't ever break from fatigue in an engine.