LASORS is always a good place to start.
I think there are five differences for a SEP (or even six now, see below)
VP prop,
tailwheel,
retractable,
pressurised,
turbocharge.
All are covered by a sign off in your log book. As far as I am aware it is at the instructors discretion what training is given.
IMHO VP, retractable, turbocharging and pressure are all a non event (and it is even doubtful whether they should have been covered by a difference given that in any event you would have done a number of check rides before flying a new aircraft of this type).
Tailwheel requires rather more time on tailwheel aircraft to become comfortable.
Of course in the old days difference endorsements didnt exist.
Happily, if you logged any of these differences in the old days, grandfather rights apply to the new days.
IMC, IR, night, multi are all type ratings not part of difference training. Some more sophisticated SEPs are covered my type ratings (notwithstanding that you might have difference endorsements for pressure, wobbly prop and undercarriage) - Malibu for example, and glass screens and possibly G430 and G530 are now considered to constitute differences (depending how you interpret the legiislation).
.. .. .. and I have probably got half of that wrong, but I thought I would have a go
- the experts will be along in the morning
.