My setup will work in your GT350R.
I had a GT and not a 350/350R.
The seat mount is Planted Technologies.
Your harnesses are secured through the roll bar, (mine is the gray finished Watson bar) and eyebolts attached to factory chassis mounting points. You can retain stock seatbelt...
I can take a photo and PM you. It is a steel side mount made by Cobra.
Everything purchased at Subesports in Huntington Beach.
Cobra Sebring Pro Fit (GT model - slightly wider) https://www.cobraseats-usa.com/motorsport/sebring+pro-fit
Planted Technologies floor mount
Cobra side...
I'm 6'2" (long torso) 32" inseam.
I fit comfortably with room to spare with an Arai GP5W helmet and Schroth Profi 6 Hans harnesses.
You can delete the slider and just mount it direct to the side mounts to lower the seat an additional 1" or so.
Let me know if you're interested.
For Sale is one (1) qty Brand New Apex Raceparts EC-7 18x10 et43 with a Brand New Continental DW 275/40/18 mounted and balanced with 0 miles on the tires/wheels. Brand New.
Located in Glendale, CA. Purchased 5th wheel to be used as a spare. Never ended up using it. My loss is your gain...