Airshocks are an inexpensive way to go. My friend put a pair in the ass end of his 65 Mustang so he could get a racked look. He drove around with them up all the time. In fact, His rear suspension was so old, it was really bouncy and couldn't support the weight, so if his airshocks were down, he couldn't drive anywhere.
I don't see any problem with you doing it like that. I don't know how much lift you will be able to achieve because obviously, your stock suspension parts will limit how high you can go. I don't think you will be able to go higher than an inch or two in the front. You might have to buy lifted control arms. They aren't too expensive. For the rear, lifting blocks are very cheap. You can get them for as cheap as $30. I am not familiar with what suspension setup the 94 Jimmy's come with. Spindles or Control Arms in the front and Leaf Springs in the back I would assume. Let me know if you have any other questions.