This can be done too, but it is a significant amount of trouble. It appears that most people purchased the front end they wanted with their car, as information on this modification is limited.
According to Paul Bratina:
"The following parts must be replaced: hood, fenders, headlights, side marker lights. The front bumper can be kept (as in my case) but must be slightly modified. Replacing the bumper with a 92-94 makes the conversion easier. Replacing the hood is strictly bolt-on. The fenders are bolt-on except for where they attach at the very front (easily accommodated). Mounting the headlights (and to a lesser extent, the side marker lights) is by far the hardest part of the conversion, and is definitely not a bolt-on procedure. I certainly wouldn't consider it technically difficult. Mostly just time consuming.
I think it's worth mentioning a little bit about the costs involved in the conversion. First, assuming you get all the parts necessary at the wreckers, the parts alone would run somewhere in the $500-$1000 area. (Of course, some of this cost could be recovered with the sale of your old parts.) Then you have the issue of repainting the car. Unless one is interested in a multi-coloured car (all the various body parts that were necessarily replaced), I consider repainting the car to be absolutely mandatory. So whatever the paint job costs, could theoretically be added to the cost of the conversion. In my case, I was going to be repainting the car anyway, so that cost didn't "count". I really feel the thought process on this conversion should be something like: "I'm going to get the car repainted and while I'm at it, I'll throw in a conversion." Not the other way around--you know, do a conversion and throw in a paint job."
A quick & dirty method for keeping the headlights down is to remove the fuse that controls the headlight motors, or to rewire them under manual control. This keeps the lights down when they are on, and thus is sort of a 'non-popup' mod.
The Last Word:: George Johnson adds:
"I looked for what I believed to be a good amount of time for the popup to non-popup conversion wiring schematic. I apparently failed to find it, so I figured you might like to add it into the answer to the swap.
Solid Red Solid Red
Red w/Blue Stripe Red w/Blue Stripe
Red w/White Stripe Black
Turn signal/running light assemblies will interchange." [Thanks, George!]