We got an 05 3800SC from an Impala sitting in the garage and it looks just like the one that's in my 87GT which came from an 06 GTP with the exception that it's a series II. You will need to move or relocate the coil pack regardless of which engine you have, swap valve covers as suggested, and reverse the direction of fuel flow to/from the rail. I've reversed the series III rails w/o any problem but don't know if the series II rails can be reversed with the same amount of notching and fitting.
I agree that the oil filer adpaters should work in most applications. If you are doing a stick swap you'll need the 96-98 3800 F-Body (Camaro) flywheel that must be machined and balanced to fit.
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87GT 3.4 Turbo- 0-60 5.2 seconds
2006 3800SC Series III swap in progress
Engine Controls, PCM goodies,
re-programming & odd electronics stuff
" I'M ON THE LOOSE WITHOUT THE JUICE "