As an update to that...
I tried copying more stuff to a folder on my Win7 machine just now -

signtool.exe and all of the DLLs from the

c:\program files (x86)\Windows Kits\8.1\bin\x86

folder.

And now invoking the 8.1 signtool from that folder that also has all the
DLLs, it did sign and timestamp an .exe using a 3161 server
(http://timestamp.comodoca.com/rfc3161)

Playing a bit more, it seems that the new signtool.exe only actually
requires the mssign32.dll file.

So it looks as if you can grab the tools off an 8 or 8.1 machine and make
them work on Win7.

But YMMV and comes with the usual two foot guarantee ;-)

Jane