dude i used a 5 gallon long trip tank when i first startd working on mine i didnt have any problems at all just be sure your clearances are ok and the tank isnt sitting on the head or carbs or anything and it should be ok but sometimes mounting can be tricky i got lucky mine bolted up (i bought it blind as i needed something to put gas in besides a solo cup for tuning purposes ) but be wary if you get one that big they can make the bike top heavy in a bad way
peace
Jimmy