The fronts are the same as the TR6. But on a TR4, the rears are screwed in from the front surface of the hub and then peened over on the back surface to lock them in place.
If you use replacement studs on the rear (i.e Dorman), Dorman provides a specs for hole size, shoulder length, et c.
To replace the rear original studs, you'll likely need to remove the axles with the hubs still pressed on as this method would be much easier than also having to remove the hubs from the axles. Make sure that you keep the shims from each side separate from each other. If you get things mixed up, it will mess up the R&P mesh in the diff. So take notes as you go.
I removed the peening on my rear hubs *axles NOT attached btw* by punching a center then using a large drill (might have been 5/8" IIFC)on my drill press to gently cut away the peening from the surface. Since the tips of a big drill is wide, it will cut the peen rather than drill through. But, take it slow and be cautious not to drill the hub - at all. When you're close, try backing off the lug using two nuts locked together. It might take a little grinding with the edge of a 3" cutoff wheel to remove enough peen so that you can back out the lugs.
And if you're planning on using original method rear studs, the axles have to come out so that you can peen over the backside.. But some have use JBWeld - not me.
To peen I used a dull cold chisel and hammered a pizza slice pattern on the end of the threaded portion of the lug that screwed through to the back of the hub until flattish, just enough to capture the thread in place.
Hope this helps.