is alldata just for that exact model or could i customize it for the engine i have in it????
like instead of an 89 with 2.8 tbi would it let me choose an 89 2.8 carbed???
what size carb does it have on it anyways????
or sould i stick with haynes for a wide range of blazers???

 

Only what was offered in that particular year. You would need to get two subscriptions, one for your truck and what it came with stock, the other for the engine and what it came in stock.

 

Haynes has always worked for me...unfortunately sometimes it can be too vague. Personally I have never used alldata, but from what i hear its a pretty reliable source

 

Haynes or Chilton is about the only things that will cover both, but as stated above, they will be lacking in the detail. Factory service manuals are going to be $$$. You could try grabbing one of those GM service DVDs off of eBay...