hey, got a problem. I bought this ta new and drove it for a few years and then parked it.it has been in storage for 20+ yrs. I recently pulled it out to sell it as a numbers matching car. first guy that comes to seriously look at it says it is not # matching. the casting number on the back of the block is 485428 which is from 71 to 74 and not the 500813 for 75. the wx is on the front of the engine below the eng. serial number. build date is 07/75 .could they have used a 74 block in the very begining when they (pontiac) decided to put the 455 into these cars half way through the year? HELP!!!!

doug