Diff Housing Narrowing In SoCal
Sutton engineering in LA Habra did a narrowing and resplining of an 8 3/4 for me for a v8 vega.. It was many years ago, and according to yelp, they have closed. There is another Sutton engineering in City of Industry, but I don't know if it's the same or different company.
There's always Currie, but they do almost exclusively 9"fords, and I hear they are expensive. If they will do the job, it'll get done right.
(To be perfectly honest, personally I would consider a narrowed Dana or nine inch from strange or Dr Diff, before I put a load of money into an 8 3/4).