def. tranny first, most important.
then like the other guys said:
tie rod sleeves
shim kit
possibly centerlink
clamping your rear springs
you have gauges? def. need an EGT
Twins are great, and Nathan's (MPI) are some damn fine work.
My best piece of advice, like Eric Merchant told me years ago....
"Overbuild it, don't underbuild" that is so true in the tranny aspect and the twins as well.
I'm on my second set of twins and already wanting a bigger set, this stuff is so darned addicting.
Best of luck.