Rich I'm not too sure if theres such thing as "too big of a cage"... His looks pretty close to the same as the ones Ive built and I have 4 snakes in cages like those with no issues. The cage may be a little large for a baby but I wouldnt rule it out just yet... Every snake is different so you dont know until you try it out. Since he already has it built I would give it a shot... worse comes to worse you spend 10$ on a tub and move him over... I house my babies in 66qt tubs and they work just fine... again I have pics of my setups in my gallery if you wanna check em out...

Like becky said the heat panels are a great idea... I was going to go the same route but I have 10 snakes so 10 heat panels at 80$ a pop isnt worth it... I just heat the whole room to 79. If you only have one and dont have the option of heating a whole room id go with a heat panel.