okay so the stock trans in my '99 gtp is basically shot. I got a free trans from my teacher at school. Im like 99% sure its a 4t65e, but im no trans expert. The trans I got for free needed rebuilt, so i tore it apart and nearly all the clutches were burnt up and felt gritty. The wavy imput clutch was also broke in 3 pieces. I ordered a master kit w/steels + a new wavy imput clutch. The trans will be getting put back together tomorrow. I ran what i believe the casting number through google and I believe its out of a '98 regal. The number I got from the trans is:

GM-B
24209508
923

Can anyone clarify what this trans was pulled from. And if it is from a '98 regal will it bolt up fine to my '99 gtp (cooler lines and all)?