I am betting that your client would not like to see you rebuild his cabinets, drawers, etc., and just wants better working drawers. Yes? No?

Most of my clients (especially my commercial guys) always cast a strong eye towards the balance of utility to price equation and will almost always take what they perceive is the best bang for he buck.

Just a thought here, another look at the situation.

If they are happy with the drawers (heavy built, doing the job) and aren't interested into making their sack drawer into a piece of cabinetry, why don't you replace the slides and be done with it?

They sell these slides

http://www.homedepot.com/p/Liberty-2...ZP-W/202200646

under different names, but the ones that they sell at HD and Lowes are now branded as "Richelieu" and "Liberty" and almost all the upper end products from those two companies branded as such are the old Accuride products. I like KV, but also like Accuride and have used their products for years as we had a supplier here for years. I used the Accuride products in kitchens and some commercial and never had a kick about their durability.

And if you leave the spacers on the drawers, you could like a hero to your client if you can find a slide with the same dimensions that would be a direct replacement. With a purchase from the big box, you could simply return the slides if they don't work.

Personally, having run into the situation you are in now, I left the spacers on the drawers as somebody else took the time and effort to shim out the sides (reason to me unknown, I think they didn't plan for or get the right slides) to make the drawer slides fit. I did a straight replacement and was done with six drawers in less than a half day as I had to put a couple of blocks in the backs of the drawers to receive the end of the slide that was inside the cabinet.

My client was pleased with the drawers and pleased with the price.

Robert