Chris,
Only the previous owner will know what the additive in the fuel was, but as it was red, I would hazard a guess at Redex upper cylinder lubricant - this would give some protection to the tank without causing any other problems when it subsequently gets drawn into the engine.
Regarding the rocker gear - this relies totally on mist lubrication once the engine is running. If the bike has been laid up for any length of time, I would suggest that it would be a good idea to go round the valve gear with an oil can about 12 hours before trying to run it. If the valves/guides or rocker spindles have dried up, it is a waste of time pointing the oil can at them immediately prior to running, as the oil wont have chance to penetrate. Bearing in mind that there is no positive oiling, I make sure everything is well lubricated on assembly. As to the amount of oil you would expect to find in the rocker boxes - about 1 teaspoonful as you remove the cover, and the internals just 'wetted' with oil. If you have removed the rocker blocks in the process of taking the heads off - replace the spring washers on the head studs with another plain washer, and seat the rocker blocks on a smear of 'instant gasket'. This will prevent oil from getting under the blocks and eventually finding it's way down the head studs and quite effectively waterproofing your boots!
Regards,
Eddie.