Hmm, I think it might be dead.
Finally got around to fitting it today and although the power light comes on, there is no monitor output or floppy activity.
Putting the original CPU back in the machine works as normal so I didn't damage the socket or anything (even used a n extractor tool like a good boy).
Disappointing, but not the end of the world...
1977 VCS Heavy Sixxer (Boxed)
1990 Atari 1040STE, 4MB, UltraSatan, TOS 2.06, TT Touch -> Atari SC1435 Colour CRT Monitor
1991 Atari TT030, 2/16MB, Int 8GB Gigafile, TOS 3.06, CaTTamaran Accelerator -> 1991 Atari TTM195 19" Mono CRT Monitor
1993 *** NEW! *** Atari Falcon030, 14MB, 84MB HDD, TOS 4.04
Amiga 500, Win 3.11 PC, Several old Macs, Newton, SGI Indy, much more and counting!