That one looks like an old kildakin.. the outside is just a protective layer and really wont make too much difference to whats goingon on the inside. Make it pretty if you want though
I vote for using it as a kettle. If you are planning on using kegs as teh basis for your system... then you wont find too many that are bigger than 50l. I reckon you want your kettle bigger than your HLT, so get another normal keg for HLT and use the bigger one for the kettle.
If you are willing to pony up the cash for a proper pot as your next vessel though, then I say use it as a HLT and use the actual pot as your kettle.
I will however add my voice to the brigade that is suggesting BIAB. I brew using both BIAB and a traditional 3 vessel system. Heres why I suggest that you go BIAB.. for now at least.
You already have 75% of what you need. The Keg as your kettle. All you need is a burner and $10.00 for bag material and you are basically there.
You could already be brewing your first AG batches when otherwise you might still be looking around for the "other" two vessels.
If after a few brews, you decide you would rather go traditional, you have probably only spent $10.00 that you wouldn't be spending anyway, so its a no-lose proposition
You can "learn on the fly" IMHO the BIAB technique is so much less complicated than a trad brew, that it gets you going, brewing and learning from experience very quickly. You can brush up on theory and different techniques, while you are drinking your first brews.
As I said, I brew both ways... and I will basically never recommend that someone "enter" the realm of AG brewing via a 3 vessel system again. I simply feel that BIAB is a MUCH more appropriate technique for begginers.
And if you want more... then you move on with virtually no disadvantage, having gained a bit of knowledge on the way.
Either way, that keg is a great score. Good luck.
Thirsty