yes a 25box is a good idea. the syncros a only a bit more efective but. if u smash the gears with button clutch it will pop.
a good one is the 34gtt box. beter syncro design and uses a bigger clutch.(250mm vs 240mm but pull type)
to fit it in the tunnel is a bit of an exercise. is ai origonaly an auto? they have a bigger tunel.
getting the corect drivline angle is very important.(getting the back of the box high enough)
not somthing that id do in my driveway, but much more thrashproof.
mx7 gearbox is the same size but has shit syncros and even worse ratios.
unless you want to run 3.4:1 diff ratio