Just wanted to pass on a lesson learned. With nearly 200 thousand
miles on my 94 Safari, it was time for new shocks. I went out and
bought new shocks. No problem, just unbolt the old ones and bolt on
the new ones. Wrong!! GMC Safari and Chevy Astro Vans are the
hardest vehicles on the road to remove the front shocks. After
skinning knuckles and mumbling numerous cus words, I decided to check
the internet for advice. I found a really cool tool called
the "Shock Buster". It basicly breaks off the old shock nut in under
30 seconds. You can change out a front shock in under 5 minutes.
The product worked as advertised. It is a little pricey at $65, but
worth it if you do your own maintenance as I do. It also works on
almost any car, truck, or van. www.shockbuster.com

I actually just did the same thing on my 94 safari. Like yours, the top shock nuts were totally frozen. However, I just grasped the piston (within the spring) with a locking vise grip (using a rubber 'jar lid opener' between the shaft and jaws of the vise grip). Once it was locked on and tight, I went at the top nuts and basically twisted off the top nut. Same effect, cheaper tools.