The springs should work on the Tamiya Cars. I believe they should work on the HB shocks as well. They are the same dimensions as AE springs, so if you have an AE spring handy and they fit, then ours should too.
I have a buddy who has tried them on his Tamiya and they fit nicely, this is confirmed.
As for the pistons, it is easy to find out. What are the dimensions of an HPI/HB piston? Ours are 10mm in outside diameter, with a 3.15 mm shaft hole, the height of the piston is 2.45mm.