Gas tank for the pitbull

been considering modifying the pitbull to change the gas tank and mount the speedo on the handlebars.
Found a few gas tanks online that are very resonably priced.
Just wondering if there is something that I should look at before purchasing a new tank? Other than fitment I know I am going to have to modify the frame a bit but as far as the tank is concerned anything to look into ? I.e. Tank lining etc
 
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