Buying Advice- Purchasing a '97 AWD Astro w/o Front Differential ?

Wow! That would be a large project, but certainly possible.
One question: Are you wanting a true 4x4 conversion from an AWD, or are you wanting a AWD conversion van? It is just a small bit of semantics, bit it does make a difference in the end result, and in what you parts will have to locate.

I was somewhat surprised the front diff is actually "gone", but I do not see a front diff in the pictures, nor do I see an axle.
How are the hubs held together, ...just the axle stub and the big nut?
Something in the translation does not ad up for me.
I just went out to look at mine( 1998) , to refresh my memory about what I thought I should see in the pictures.
I would definitely want somebody a bit more knowledgeable to look it over, to see just what is, (or is not), there.
Is the transfer case still there? If so, it is probably no good either.
It would take almost no time to see how the front hubs are held together, if one knew what they were looking at.
All the necessary parts can be had from local yards, but the labor to install everything will be quite expensive.
I am guessing in, California, the labor would run at least a couple of thousand dollars just to put stock pieces back in place.
Depending upon the source, a set of necessary used parts ( Diiff, Transfer case, drive shaft, and some misc hardware) and a pair of new axles ( you should spend the money on new axles, because used ones are a gamble, and you do not want to have to pay labor to immediately replace them again) could probably be found for less than $1000, but it could run much more.
Replacing everything is not technically difficult work, but is time consuming and requires a fair amount of tools and significant physical effort.
Rod J

Have you ever pulled suspension parts off a van at a junkyard?
How about driveline? An engine? An entire sub-frame?
Heck, have you ever pulled any parts off at a junkyard?
Have you ever been to a junkyard?

I would avoid this van like the plague.
The fact it wasn't repaired correctly is a RED FLAG!
Who knows what else was "rigged".

That's a lot of money for a faulty broken van.
And it will be a money pit with loads of needed work.

Replacing the entire AWD system would be a nightmare.
Beside the ridiculous amount of work and expense, do you have your own shop?

I say.. don't walk away... RUN AWAY from this one.

Learning to do your own work on these old vehicles is the only way to go IMO. Things get expensive quick if you are paying someone, but at least there are a ton of great resources like this site

People sometimes do some crazy things if they have an issue, could have had a leak which destroyed the front differential and they removed it. Could have had a problem with the AWD case as well.

If it's an awesome price and in great condition, everything else checks out, it could be worth paying a mechanic to install a front differential and shafts. Junk yard front diff and propshaft is not expensive, the other two shafts I would probably buy new. Should be less than ~$300 in used parts depending on what ends up being needed and where you buy, another $100-200 if it needs the transfer case as well, plus installation figure on about ~4hrs or so. If you can budget $1000-1500 for that and still be happy with your purchase price, I think you could find a win there.

Personally I always recommend sticking with AWD for most people, their main usage case is water/slush/snow and only go with the 4wd TC if you really need it.