Your 800W PC P&W will be more than enough to power this rig; no worries there.
For the HS/F, you can get an adapter bracket for your current one here, but if you weren't happy with it's performance on your current rig, I wouldn't expect you to be happy with its performance on a new one, especially since the i7 probably puts out more heat than your current proc (also, lapping usually only gives you ~5C compared to good thermal paste, iirc). Personally I wouldn't go with the one you have picked out, because of the all-aluminum construction; copper has a much better thermal properties than aluminum, for HSs. I would recommend one of these:
Scythe MUGEN-2 SCMG-2000
ZALMAN CNPS9900LED
Scythe KATANA 3