I wonder if they are doing just low heads though, as per the Indy ones that I bought a few dozen of and swear by, same height bottom, just half the height in the top, so you start with the truck still sitting at the right angle and height from the bottom bushings, but the lower head means you can have the nut on nicely and still have the super loose feel, or as I have done, tighten them down a bit more and angle grind the kingpin head off a bit for a ton of clearance.
From the site, the Ace low are lower in general but still fairly tall.
Low Bushing Set
Top 10mm tall | 91a hardness
Bottom 12mm tall | 86a hardness
Classic Bushing Set
Top 12mm tall | 91a hardness
Bottom 14mm tall | 86a hardness
As I had posted earlier in another thread, but this time using Ace aftermarket measurements:
Ace low
Total 22 mm
Top 10 mm
Bottom 12 mm
Ace classic
Total 26 mm
Top 12 mm
Bottom 14 mm
Venture stock 94a
Total 22.5 mm
Top 9.5 mm
Bottom 13 mm
Thunder stock 90a and aftermarket (same) 90a, 94a, 95a, 98a, 100a
Total 23.5 mm
Top 9.5 mm
Bottom 14 mm
Indy stock 90a and aftermarket (same in both cylinder and conical) 78a, 88a, 90a, 92a, 94a, 96a
Total 23.5 mm
Top 10.5 mm
Bottom 13 mm
Then Indy low head bushings 92a
Total 21 mm
Top 8 mm
Bottom 13 mm
* Added Venture in here as well.