RG-8X is a bit larger in diameter but has a bit less line loss at greater than airplane length differences then RG-58.
At 15 ft and 120 MHz, RG-8X loss will be 0.54dB. Where RG-58 would lose 0.63dB in that scenario. Negligible and not worth worrying about.
What is worth worrying about is bending radius. RG-8X minimum bending radius is 2.5 inches. RG-58 comes in at 1 inch. Those are one-time limit bend radiuses, I’d rather not bend to the limit in airplanes.
The difference in bending radius is primarily because RG-8X has a foam dielectric core. RG-58 has a solid one.
So all things said. I’d say it’d work fine, but I would personally use the RG-58 because of the superior bending radius which is important in aircraft which have less than ideal amounts of room.
I work with different coax types quite a bit in amateur radio. I avoid the hell out of both RG-8X and RG-58 because of loss issues at greater distances (not a factor in airplanes). RG-8U is a bit better. I prefer LMR-400 for VHF work if cable distances start pushing north of 50 ft.