I take it the 87 does not have rear lockup control? My 93 2wd does not but the 94 4wd does.
Keep in mind the front brake line runs through the rear proportioning valve so that needs to be routed directly.
If you do run without a prop valve and get some rear brake lockup then swap in the 2nd gen front calipers, that should give enough increase in front brakes to do the job.
Even a set of grippier front pads may be enough. I run Hawk HPS pads on my 94 MM and 95 SR. Allot more grip than what the trucks came with.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.