My plan is to get two of the same height (about 38") and width (about 20") and have a "top" built for them to make a work bench that I can pull a chair under.
Any suggestions would be greatly appreciated.
Reading what you have written - ie - that you do not do your own mechanical work, I don't see the need for two mechanic's type "tool boxes". If you use buffers, polishing supplies etc - then perhaps two cabinets with adjustable shelving would work better for you. No reason you can't suspend a desktop between them, or just buy low profile cabinets.
Doesn't sound you will need or use a bunch of 1, 2, or 3 inch tall drawers. Perhaps a couple of cabinets with shelves and others with "mechanics tool drawers".
http://www.garagejournal.com/forum/showpost.php?p=1650420&postcount=43
Even better - how about cabinets with full extension "shelves" or drawers.
Pictured bleow is a LISTA Cabinet - this one is too large for your use - but I show it to give you some ideas of what LISTA may be able to supply on a custom basis. The point is this cabinet has doors that glide side to side, with full extension drawers {shelves?} that are fairly open. With lots of space between the drawers for tools like buffers, drills and other typical home use power tools. Many of which come in their own blow molded cases today.
Cabinet doors that slide side to side for access - saves floor space because the don't have to swing open out into the garage. Full extension drawers, in place of shelves - allow easy access to items in the back.
Lots of options besides the typical Snap-On or LISTA mechanics type tool boxes.
good luck,
Carl B.