Thought I'd do a guide highlighting which Audi models had a timing chain or Cambelt driven 4.2 V8 for reference.
All C5 models equipped with the 4.2 V8 excluding allroad is belt driven which is much better to service, and All D2 A8,S8, and D3 A8 up to 2006
The models that use the modified FSI chain driven 4.2 V8 engines are the C5 Allroad (BAS engine code), C6 A6, D3 A8, and A8L starting in 2007, S4, RS4, Q7.
An engine pull is required to service the timing chain on these FSI units due to the location being at the back of the engine next to the firewall.
overall the belt driven engines are better serviceable and also have less issues if well maintained.
The chain driven 4.2 is known for overheating issues and timing chain issues.