Final drive question???

[Godfryness]

Hi I am new here and I don't even own a Yaris but looking everywhere it seems you guys/gals may have the answers I need.

I have a 2006 Scion xB Manual transmission. My 4 gear is now poping out and needs to be fixed. I drive a lot of freeways of 70-80mph about 80% of my driving. I am doing 25k miles a year. I love this car but don't like doing 4k rpm at 80mph. I read a forum where a guy swapped in an old Corolla transmissions with a higher final drive and said it was night and day better for all round driving and way better for freeway speeds. His rpm drooped 500 at 80mph.

I also live in ut and drive in the snow a lot. So I want to put in an LSD at the same time I fix this problem. I had been looking at c160 with LSD for a swap. But the c160 final drive is so low even with the 6th gear being taller it's really no different then my gearing now so by doing the c50 to c160 swap I only gain more gears to say in a power band and an LSD but no lower RPM for cruzing.

Is it possible to swap out the final drive in the c160 with my c50 or will that not work? If no is there a higher final drive to be had for a c160 that is not crazy expensive, like from another MT I can get at a junk yard?

Is my best bet to swap out my final drive in my c50 with the Yaris FD, fix my 4th gear poping out problem and put in an LSD? If I do that what LSD will work? I am unsure if the FD Yaris is a 6 bolt or 8 bolt like mine. If it is 6 bolt that would be a weekend part correct?

I am new to all this so any guidance is very welcome and sorry if this is all posted in the wrong place.

Chad