The tubes are approximately 400mm long from fitting to fitting. In the ROG Strix Helios, that's easy for top mounting or tubes-up front mounting, but tubes down might be harder. Front mounting your GPU on a riser cable would probably be required to make it reasonable to mount tubes-down. The GPU will be kinda in the way if you have a typical big 3 slot and 3 fan current generation card (e.g. nVidia Strix 3070 or Radeon Strix 6700 and above). I can't say for sure in the Lian Li case, but the tubes are a pretty good length to give you decent options in larger cases. Beyond that, I'm very happy with my Ryujin II 360 in the Helios; it's a premium price point but seems like a very good product overall, nice build quality, etc. It works well with a Ryzen 5950X sucking in about 200W electrical power and putting out the corresponding heat. I have mine top mouted in the Helios, tubes-front on the rad, tubes-down on the pump. I'm using a LINKUP PCIe 4.0 riser cable for my GPU (the Strix one is only PCIe 3.0, sadly), although you should check if Lian Li do one suitable for your case; chosen partly based on EKWB using a LINKUP riser in one of their products and trusting them to have chosen wisely. Get yourself some spare premium thermal paste to go with it (I'm using Noctua NT-H2); the paste supplied on it seems just fine, but you may well end up refitting it several times before you are fully happy with the orientation of everything.
Tubes-down is frankly misunderstood and highly overrated, in my opinion. The Gamers Nexus video about pump vs tubes is misinterpreted by many people. The key thing is to not have the pump as the highest thing in your configuration. Tubes-up is really just fine as long as the top of the radiator is higher than the top of the pump; you would need to lose a lot of liquid volume before that started feeding air into the pump. If your radiator is mounted about as high as it can go, roughly level with the top edge of the motherboard, there's more than enough height to keep the air out of the pump, especially if you mount the pump in the default orientation with tubes running from the bottom of it. That's just me guessing on your motivation for tubes-down, and my own interpretation and opinion on that issue. If memory serves, I think Jayztwocents did a video discussing it and saying roughly that; and Steve from GN may well have done a followup to clarify the issue. The one thing you need to avoid, if possible, is something like mounting the radiator on the bottom of the case or so low on the front that the pump is partially or fully above the highest point of the radiator (which basically guarantees even a small amount of air is likely to gather in the pump and cause cavitation).