I think you'll have a hard time finding somebody to downgrade. You may want to watch the "power adders" section of the corral classifieds. I've seen trades like this before on there!
How much boost are you looking for? A-trims are pretty tough little blowers, and can be pullied up for more boost. Some of the mustangers run 'em up to 10 PSI, but I think 8 PSI is more realistic.