It’s not about being a fanboy or not, your comparing a small top chest drawer thickness to a newer box that was powder coated, so the measurements are not telling the entire story. With that said… Yes those top chest drawers where pretty thin, I believe the exterior wall frame should be double walled and fairly stout. I’ve never owned a New box till I purchased the 73” Icon, I own a Snap On Roll cab from the 70’s, It’s a monster in regards to build quality, Even at 50 years old and friction slides it holds a ton of weight. It’s not Blingy like the Icon, paint is faded to a dull orange, takes two hands to open the drawers but it was cheap.
Good luck on restoring your grandpa's box, it’s been 10 years but I was able to secure slides via snap on for like 1.50 a piece. They offered to cover it under warranty but the Box was older than I was so I chose to just pay out of pocket.