i have serveral different modded diffs in my savages.
one of the last things i have done is the 9T/29T bullet proof bevels combined with the kyosho IF103 plastic diff cup with the steel ring and the little sliding blocs. so there are now 8x16mm bearings on both sides.
How did you get the sliding blocks in there? Pics??
the IF103 cup is available e.g. at amain.
those sliding blocs are smaller than those in the hpi aluminium cup. you can see them in the second pic above. you need to modify the cross pins at the ends and produce some small blocs on your own.