Chally 1 is a strong tank and should do well in that mission and spot easily if you ...
I've been taking the Chally + triple Repair Kits, and just driving as close as I can to enemy cap zones, and proximity spotting everything, in my British Bunker.
It works (ie i get a blue star) about 50% of the time, which isn't enough. The times when it doesn't, a vehicle just does so much damage, usually a ramka, that all my spotting isn't enough. Or there's another heavily armoured vehicle in the game, who realises what i'm doing, and does it as well.
I pretty much have most of the tanks, basically all the AFV/TD/LTs, but not many mbts above T6. and a few new ones. Not too many prem vehicles. I am a sneaky spotter person too, usually.