Alright so I have an 87 cheap model (steel 14" wheels) rust free I bought to replace the body of the 88 GXL auto I have had for years. It was from up north and got tired of repairing rust damage. Brake and fuel lines etc. So the GXL is the doner car. I am moving every thing to the 5 speed car...Swapped motors and front brakes to 4 piston off the GXL. Also used the bigger GXL front sway bar. Here is the question... Was talking to the somebody at Mazdatrix and he said just pull the whole subframe and just use the 3.90 rear as is. I must admit looks like pulling the sub-frame looks like the way to go! The 87 has the 4.10 I want the posi so has anybody here used this gear with the 5 speed? I know it will take a little away but performace shouldn't be that much a facter with a N/A should it? Besides looking for better MPG.

I would rather have 4.10 and open diff then a 3.90

pay a shop a few bucks to put the 4.10 gears on the lsd unit and put it all back into the housing.