Need a new radiator 99 Firehawk

I need a new radiator. I went to O Reilly's & Autozone. The radiators they had for 1999 Firebird LS1 Manual transmission are different from the transmission I have. I bought the car late in 99 is it possible they put a 2000 radiator in my 99 Firehawk. The other problem is a radiator for a 2000 LS1 is not available. I have not checked with the dealer yet. Can someone advise me as to where I can buy a direct bolt up radiator. I have already looked at Summit and I am not sure if I should order the Proliance 432399 which is for a 99 LS1 or the Proliance 432421 which is for a 2000 LS1.