I agree: EGT/Boost/transmission temp. I have, and love, the Westech EGT/Boost combo gage on the Mopar SRT-10 pillar. I don't have the transmission temp yet, will probably put it on the steering column. May just be me, but I have a problem with drilling on the exhaust manifold with the engine running. Ditto the air blower in the exhaust pipe idea. It adds a complication and doesn't feel right. The only thing that can really hurt you is drilling the pilot hole. A little misalignment here or there and the bit can break off into the manifold. Bad news. Geno's gives you decent instructions when you order from them, but they are not Machine Shop 101. Previous experience/skill is recommended. Use grease liberally for drilling and tapping. Stop and clean the bit and tap, regrease often. Stick a pencil magnet into the hole to pick up shavings. This gets 99. 9% of the shavings, the rest are a non-factor. Most of the shavings come out on the first sweep. Above all, go SLOW, the weight of the drill plus just bit of pressure is enough. I disagree with Genos's instructions to use the 5/16" bit for the (recommended) 1/8 NPT tap. This is barely big enoug to start the tap. Use the proper "R" bit in accordance with the chart. Any doubts? Bring the truck to a shop to drill and tap the hole, clean out the shavings, put in an 1/8 NPT plug, go home to do the rest.
Good luck.