I recently started into chainsaw milling and started with a stihl 461 (76cc). It did the job but I had to push it pretty hard in the bigger wood (26”-30” stuff). I recently upgraded to the husky 3120 (120cc) out of fear I was going to melt my 461, I want to have it for firewood cutting too.
Keep in mind this is with an Alaskan mill and not milling by hand. Still a 40cc saw seems a bit small to me for prolonged ripping use. I imagine you could do it in a pinch with lots of breaks and keep the saw idling to cool down. If you have the desire to get a bigger saw I imagine you would be much happier, more power and easier on the saw.
As for the ripping chain I don’t see the problem free handing with it, I haven’t yet but I plan on it as I have a bunch laying around that will go on the firewood saws eventually. I may change the grind on it a bit, but nothing drastic to start. I also use a standard full chisel cross cut chain when milling and it works fine, I’ve got some very good results. It’s quicker and with the right control a very good end result, slightly rougher finish than the milling chain. You can also slowly grind/file your cross cut chains into ripping chains, that’s what I have started to do lately.
I hope this helps. I imagine you will get more advice from some of the really experienced helpful members on this site. I’ve been really grateful for all the help I have gotten here .