90 Gallon Tank Frame

Hi everyone! I'm brand new to this forum. I've come for some specific advice about a second-hand aquarium I just bought. I found a really cheap 90 gallon tank on a craigslist type website. The dimensions are EXACTLY 48"x24"x18" and made of 1/2" thick glass. I have seen that the tank will hold water filled to the brim, and overnight for that matter. The person I bought it from didn't tell me much other than they were given the tank by a friend and only ever housed a lizard in it, never fish. The problem I'm having is that they melted the top frame with a heat lamp and now it's a bit ugly for my taste, the middle brace is missing which is my bigger concern of course, and that the frame in-self is not one continuous piece of plastic it is 4 separate lengths of plastic. Could this have been a custom made non-manufactured tank? I've checked with "aquariumframeswholesale.com" or Over The Edge and "glasscages.com", both of these websites told me that their frames will only fit a tank that measures up to 47 7/8" long, no longer. I would like to upgrade from my 55 gallon to this 90 gallon tank but I'm afraid to run it with the frame in this condition. What advice and knowledge can you guys give me?