I did an acetone test on a keycap from the Leading Edge DC-2014 and on a keycap from a MCK 101-FX using a small cotton swab on the inside of the caps. This is enough to determine if the plastic dissolves in acetone without compromising the function or outward appearance of the cap. I used a dye-sub PBT cap from an SGI keyboard for comparison.
As expected, the dye-sub PBT cap from the SGI board showed no sign of dissolving plastic when in contact with acetone, consistent with the cap being made of PBT.
The caps from the Leading Edge DC-2014 and MCK 101-FX proved to be double-shot ABS -- definitely not PBT. These caps are also very thin. They measure about 1.0 mm thick on the top and side skirts, and the bottom skirt is only about 0.5 mm thick. I would like to put dye-sub PBT caps on t he DC-2014, but given its layout, this would be problematic except for the alphanumeric keys (and the odd-sized Right Bracket key that I am using as Backspace).
UPDATE: I installed the internal Orihalcon/Soarer converter in the DC-2014, programmed it to a quasi-HHKB layout, and installed a flush-mount micro-USB connector on the back of the case. Everything works just fine, and the board is quite usable in this configuration.
I like the feel and the subdued click of the blue Alps, but I prefer the overall sound of my Northgate Omnikey 101 with white Alps. The DC-2014 has a hollow plasticky sound, whereas the Northgate has a more solid sound (as I would expect, given the amount of steel used in its construction).