Cheers for the comments guys but can you please point me to some hard data about copper being bad?
I did some searching last night and a few things that came up on google books in brewing texts did not say this was the case, I even found a few references about all S/S breweries putting some copper back into the wort production process Miller in the USA still use copper kettles with stainless domes. I know that copper does not fit so well with cleaners used in modern process cleaning systems but this is only a home brew setup not a comercial brewery and if I have to clean it with a pressure cleaner so be it.
Also if copper is so bad why do distilleries still build their stills out of it?
Copper isnt bad, just depends what you're using it for. In fact i just posted a reason why it was good. Copper is put back into brewing processes probably for the reason i mentioned, natural antibacterial, and also because copper can catalyse sulfide based reactions, allowing the sulfides to be converted to H2S (gas) which leaves the kettle/fermentor as a big smelly fart rather than you having to drink a big smelly fart. This is especially true for distilleries as the catalytic conversion is accelerated at high temperatures.
This is the primary reason that distillery operators whom use all stainless stills routinely pack their columns with copper raschig rings or at least have some sheets of copper somewhere in the vapour path.
Needless to say as both distilling and beer brewing are both very old arts, one reason why some breweries only use copper for stills is none other than tradition. Their recepies date back sometimes 100's of years and naturally they are very reluctant to change.
This I guess is the same case. You are fortunate to have come across a nice massive bit of copper there, which I'm sure will would make a perfectly fine kettle/brew rig in a pinch. Most brewers and industry shy away from copper vessels due to excessive material costs, reactivity and difficulties in cleaning and maintaining. If you honestly believe these (on your scale/conditions) will not impact you, go for it, nobody will stop you or try to stop you, only merely attempt to indicate why it's not routinely done and what difficulties you may discover.
Another reason possibly not to use copper is that as it may form copper salts in solution, these can promote bacterial infection and may also affect the taste of your product however in HERMS setups your wort flows through copper so it may be moot point.
there are many reasons for and against, it appears you are actively weighing up your options by doing research which is very commendable. the only other comment I can make is that, given the success of standard 'Big-W/Kmart + Bunnings' breweries (mostly SS and brass), it seems to me, saddening to use such a unique piece of copper for something that can be made out off the shelf items for minimal cost. Hence why i think you should save it for some epic project.
dave: traditional stills and such are not tinned, they merely form a patina through use which "protects" the underlying copper from oxidation, acts as a catalyst while still retaining the thermal properties of the bulk material