I have an "old" style engine crane, from the photo, exactly the same as your Bluebird. it already has three lifting positions drilled into the inner sliding portion of the boom. you're right the wall thickness on those cranes is high.
As to bracing on the column and the outriggers, never found it necessary, they are extraordinarily strong.
With regard to the comparison between the "bluebird" and the other crane, you must remember that the other crane is cheap Chinese design to reduce material and thereby cost. When the material hasn't got the balls, you must give it a walking stick.
I'm not in the workshop right now but later on today I'll take pics of my machine for your comparison.