Hello fellow Lexus RC350 F Sport owners. Just joined and may be able to share some information.
I just installed RSR springs on my car and they look great. Only did the front as the back sat ok. I thought the RC was a little bland in looks for me, so I set out and modified it somewhat. Added 20" Rennan spoke rims front 9" and back 10.5", lowered it in the front 35mm. Had to use 5mm spacers as the front callipers were too big for the spokes, but these work fine. The rest was not a problem. Could have taken 12 " on the back. Imported a rear boot spoiler, Made some front splitter spoilers and side ones to finish it off, took rear mufflers off and put on polished stainless hotdog style mufflers with twin tail pipes. Sounds ok and look great.
I got my springs from USA on Ebay. Just check freight costings some suppliers are cheaper. RSR springs are designed in Japan and by all reports are the best. I have a pair of rear new lowered springs for sale if anyone is interested.
Hope this helps. Very hard to find anything for the RC models I have searched the world and it seems to be a car no one wants to know. Anyhow! all is well.