Either a turbo or a super charger will help with high elevation power loss. If you're not operating alot at high elevation, the motor build will be alot cheaper and less complicated without a turbo or supercharger.
On the transmission, since you're using a 429, which is the same family as the 460, you could go with an E4OD 4 speed overdrive transmission, instead of the C6. The E4OD not only has a .71 overdrive ratio, it also has lower ratio first and second planetary gear sets than the stock C6 ratios.
You wouldn't have a need for the Gear Vendors for the overdrive ratio with an E4OD, though you also wouldn't have a gear between each gear, without the Gear Vendors. It's a bit of a toss-up.
Cost-wise, it's a toss-up too. E4OD's are alot more expensive to build up right, compared to a C6.