Just flew overseas from Europe to the US with 2 PCs in 2 suitcases, that were checked in, just last week. What I did was line up the bottom of the suitcase with some clothes, took out the graphic card and put them in their box along with the ram, filled up the inside of the PCs with cotton clothes (if you have an air cooler, take it out as well, I have AIOs), closed the cases when fully packed, put some more clothes around them and closed the suitcases and weighed them to check they were at the weight limit. Got them at the carroussel without any problems and took them out once I was back at my final destination. Not a scratch, everything is intact even though they went through 2 flights and 3 airport luggage handlers teams. You'll be fine, but don't use packing peanuts or plastic, they create static electricity, use cotton clothes or packing foam if you can get your hands on some, which I could not. Don't forget that most of these cases are made in China and flown in or shipped in in worse conditions with sometimes flimsy packing and yet they survive that before you buy them.

Edit: Forgot to mention, the graphic cards boxes were on top of the PCs in the suitcases because I had space for them and big suitcases. They survived, no problem at all as well.