I took my zx5 out on a dusty polished wood floor with a sinterted 4.5 once, it was fun
As for drifting on tarmac a 10.5 with some bald tyres would probably slide a little but I dont think you would have the insane power needed to hold really big drifts, If you put PVC tape on the wheels thats a different matter as the absolute lack of grip would mean you'll slide quite easily at low speeds so the 10.5 should be enough power.
Set the suspension low and fairly solid. The diagram you have shown is for a locked diff already, usually instead of the screws there you get small balls which is what gives the differential the action, if you could rebuild the diffs with the screws like that they would be locked. Alternatively you could tighten the screw thats normally used to adjust the diff in fully, that would also lock it.
Shock oil just buy the thickest stuff you can and similar with the springs, if you cant get stiff enough springs get some fuel tubing and use it inside the shocks underneath the pistol to limit shock travel and set ride height via that method then stack two smaller stiff springs ontop of each other (TC springs would deffinately work for this, you might get buggy ones fitted on)
Thats just a few idea's off the top of my head, the easiest way to do some drifting in a buggy would be just buy a 3.5/4.5 brushless and run it on bald tyres and be prepared to melt some diffs