Hmm, a quick side trip indeed! (Ref oldsoldier's comment). Being impatient, I headed for the South Top in a direct line from the summit of Slieve Felim, but be warned that this approach involves putting up with some of that most hateful of hillwalking activities: fir bashing. Thankfully the forest isn't too dense, and the amount to be covered is less than 500 metres, but it's a pain nonetheless. Be careful not to get pulled too far to the left (east), or you'll end up half-way down the very steep valley for that river with the unpronounceable name.
The summit itself is deep heather, so lots of exercise lifting your knees high, but again, it's not for too long a distance. Some really great views over the the Galty mountains from the summit -- in fact I'd say the views here are better than for the main top. OpenStreetMap shows the forest tracks accurately around Slieve Felim; I used OSM in preference to the Discovery map. Linkback: https://mountainviews.ie/summit/795/comment/6197/

My final top in a 4-Carn loop taking in Cullaun and the three Slieve Felims, this, in my view, being the better of the Felim tops, in that at least its high point is quite well defined, if unmarked. From the track at R80840 57060 C it is a short climb, but first one must overcome an area of ankle-breaking felled forest before emerging on to open hillside, which is covered in heather. Luckily there are a number of narrow trails towards the summit, which is a slightly elevated mound of heathery ground. Good views all round. The photo shows Slieve Felim East and South tops, taken from a forest track at R819 574 E. Linkback: https://mountainviews.ie/summit/795/comment/23411/