What size split flange fits on a 95 D1?

where manifold meets the y pipe

 

Where the exhaust manifold meets the Y-pipe there are two flat faces with studs and nuts. No split flange. You might use a split flange where the Y pipe meets the exhaust pipes.

Which are you thinking of?

exhaust manifold gasket and stud kit: https://www.roverparts.com/exhaust/kits/ERR551K/

As for the split flange, I have this one in my Disco parts list but put it there so long ago that I cannot confirm it is the correct size...

 

my bolt heads broke, I got one holdin up each side. I want to use a split flange to tighten it.

do you know what size would be best?

 

I don't. Most would drill it out and either re-tap for new studs, or use nuts and bolts.