No discernable difference between proline and oem, likely same manufacturer. The oem tank is absolute crap and the exact same tank fitted into the early classics which were all recalled due to large no's of rusted/leaking tanks. They used the same tank again in 93. The issue with these tanks is the original finish. My advice would be to but the best rust preventive coating on you can. The brits often remove the skid plate when they replace a tank. This eliminates the ability for grit between the tank and skid plate to hold moisture and rust a hole in the tank.
My advice, put a new pimp in when you have it down. Sucks dropping a tank to replace a pump and again the pump isn't expensive enough to run the risk.