new member with lots of questions

[baby Gs Dad]

hi everyone i am a new member and a first time owner of an 1999 a4 quattro. i really enjoyed driving the car for the first 10 days untill the piston broke. so far i have had too replace the motor and a few other parts some by choice. i do have a question for some more experinced audi owners; the motor that came out of the car was an AEB of 10/98 and the one i replaced it with was 7/99. when i was buying parts they asked me the date of the motor and i have seen that some of the parts are different eg the timming belt could someone who knows more about this tell me the differences of the motor eg horse power is differents thankyou everyone