An iron barrel on a Dyno. You could blow it up real good for the rebuild. It will tell you max power. If it is hooked up to a sniffer it will give you some jetting info. Be very afraid of your bike on a dyno.
IMO, stock Iron Barrels don't like to run for any period of time at Wide Open Throttle.They can easily overheat. Their notoriously weak piston can crack and their lower end is far from being robust.Iron Barrels were designed for moderate riding during an era where 55 mph was considered fast on the roads so unless someone is willing to spend large amounts of money beefing up the engine I can't see where running the bike on a dyno serves any useful purpose.
A dyno will not damage a Bullet or anything else for that matter. An idiot operating the dyno can, though, as I once witnessed. Many 'iron barrel' Bullets suffer as a result of being wrapped in cotton wool by their owners, many wrongly believing that by keeping the revs low and the gear high, that they are saving on wear and tear. Wrong. I have seen many exhaust valves and seats in 350 and 500 Bullets [other machines too] which were badly burned because the machines had larger gearbox sprockets fitted and were routinely made to lug up hills in top gear at around 45 mph with W.O.T. and 'cruise' at about 60 mph on full throttle, this being almost the top speed of an untuned, overgeared 500. One such machine has just been through my workshops - 19t gearbox sprocket, loud but restrictive exhaust and MK I Amal with too large a main jet for the otherwise standard engine. This is a better way to kill a Bullet than putting one on a dyno with a competent operator. This machine also had trapped second and oil rings, coked into their grooves by the combustion gasses blowing past them - this would be a good way to overheat the barrel and piston and cause a seiziure. Big ends and mains suffer from being overloaded in this way, too. A session on the dyno will enable you to get the best from any machine, in any state of tune, without causing it any harm, but tell the operator a maximum RPM figure for the machine and get it warmed up first, by doing a few runs to about 75% of full speed RPM's, before testing for max power. B.W.