Gus/Smokefrog/Kojak,
Fabulous watch - I love the linear/curved design on the QTC/QED - it's right up there at the top of the list. A very stylish and classy "classic".
As far as I know, the Hamiltons always had stainless steel backs. I'm pretty sure that you've got the "right" case back. The Hamilton case backs look almost identical to the P2/P3 case backs except that they have both a serial number and also a date code as you've noted. They Pulsar case backs have just the serial number on top - no date code at the bottom.
Here's a previous thread on the topic of Hamilton marked case backs:
http://www.dwf.nu/viewtopic.php?t=1600
from Bruce:
"Though the parts are dimensionally compatible, remember, Hamilton never made a solid gold watch, and all of their stainless and GF watches had stainless backs. Also, they all had a serial number AND date code on the caseback [and both of these numbers always had six digits]. The P2 back has a 5-digit serial [which is consistant with the early P2s], and no date code."
-abe.