The source I looked at gave the 259 figure for the -61, with the 63 having the wings from the 62 and the fuselage from the 61, with a longer range. http://www.airliners.net/info/stats.main?id=194
Your source seems to suggest that the 62 was longer than the 61, while the other source says that the 62 was shorter than the 61.
If the 61 and the 63 were the same length, as the other source suggests, you probably could cram in 259. But remember, a planeload of combat soldiers is probably going to weigh more than a standard planeload of passengers which would include men, women and children.