for questions and answers about alternative power transplants on the T25, GTi, Porsche,Subaru etc, this is the place. You must register to post but anyone can read.
You need to find the number on the block on the flat part between injectors 3 and 4. AHU pumps had extra "ribs" on the body and were generally bosch 971, while 1z pumps didn't have these ribs and were generally 985 series. If you can't read the block code can you read the bosch number on the pump? Of course if the pump has been changed then this doesn't hold but may give you a clue...
if you're just replacing the block and head then an AHU is a direct replacement (and slightly better) - either a 1z or an AHU will fit fine and the pump/turbo/ECU combination you have will work.