KBC (or equivalent) 1-070-013 13/64 X 6" Aircraft Extension Drill @ $1.76 ea.
KBC (or equivalent) 5-016-010 #2 X 6" OAL Chucking Reamer @ $5.10 ea.
A gundrill would be ideal...but could be a wee bit pricey unless the part run is large enough to justify the cost. You're going to have to pre-drill a short pilot, too. They pop up cheaply enough on Ebay, but of course, it's a pig in a poke when it come's to finding the right size. If you choose a conventional twist drill, I'd recommend an extension drill, rather than an extra length drill, because it's mostly solid shank & has more rigidity...of course this is offset by the downside of the increased number of chip clearance peck's you'll have to make.& reduction of coolant flow. Good luck! - John