I dont think the ride quality will be affected too much as it will be set up very soft. some model falcons came with discs so no problems there. I dont think the old merc diff would be able to handle the abuse I intend to give it.
few more pics
I have the front guards, bonnet and doors stripped and they have very little rust in them, few repairs to do but i am happy
Your factory rear end will more than handle the jap engines torque and to mount the Ford 9" is , As Al rightly points out. a step backwards. The 9" diffs suck power because of the 54 year old design (yes they were designed that long ago) and you will end up with an ill handling pig. A safe in a wheel barrow is how a mate here in brisbane describes the handling of his W108 with Ford 9" diff.
A lot of mystique and BS has grown over the years regarding the Ford axle and because you are in OZ you could actually get a commodore (and cortina 6,Valiant, Falcon, Sigma ,Centura etc etc ) Borgwarner rear end as cheap as chips with dozens of different ratios and LSD configurations .They are still used in the latest HSV's .
Besides the loss of independent rear end you will be adding a huge amount of extra unsprung weight which is a sure way to kill handling. (ever tried picking up the pumpkin from a ford diff?)
Sure Falcons have them but they are crappy cars ,you have a Mercedes and fitting ford parts is wrong LOL!.
Now,to issue of power sapping,the Ford 9" is known for this and bvecause you are using an engine designed for a smaller lighter jap car you are going to be struggling to get real performance.
Why not use the merc back end until (if) it blows up?
The Mercedes 6.3 has the same diff (higher ratio and LSD) and several hundred horsepower and foot pounds of torque doesn't break them.
I recently did a Merc V8 with 300KW into a finny which is running a stock rear and it's fine . lots of abuse in the last 3 months and no sign of trouble. You should look at the axles,they are bigger than the 9" axles.. :-)
You should go over to the ozbenz site,plenty of performance upgrades going on there plus contacts with lots of spares for W108's...including me,I have tonnes of them.