I'm no pro at the forced induction stuff, hopefully some of them will chime in later.

Some things to consider with turbo's mounted downstream.
- Oil supply, you need a way to get the oil to the turbo and back to the oilpan. Not a big deal getting it there, but chances are you will need some type of pump to push the oil back to the pan, otherwise it will likely pool inside the turbo housing and blow out the seals.
- Additional piping needed. You need a way to get the cold side air charge back to the intake on the engine. With only 8-10 lbs you may not need an intercooler to begin with so this may save some. The additional length of pipe adds weight and could be an additional place for leaks to happen.
- Other things: Mounting them likely under the vehicle puts the turbos and air filters in harms way as far as road debris, etc

There are other things to consider, but for me these would be the biggest ones. Not show stoppers by any means, but depending on the chassis/vehicle you're working on its sometimes easier to just work through the issues on keeping them in the engine compartment and hiding them as best you can.

It sounds like an interesting project, a low comp steel crank RB would make a great starting point.

I always thought a cool project would be a big old mid-70's C-body like a Newyorker or Newport with a 440 and a turbo. Huge engine bays and lots of room for an intercooler.
or a 70's 1/2 ton shortbox with a toolbox mounted in the bed. Mount the turbo(s) in the toolbox and have a sorta sleeper effect.

Hopefully others will chime in with their input. There are some very knowledgeable resources here....
Murray