How about 3?
I have another set of heads I can get measurements for flanges.
My Dad has a cnc plasma cutter he built(retired engineer)
He's made a few parts, but had some programming hiccups lately.
As you well know, ss is expensive, and I would think the flange would need to be 3/8"
If you can mock up, cut and bend the pipes, I know he can make head and collector flanges, once he gets the gliche fixed.
Something for us to seriously consider.

 

If I had a shop I would do it.

 

 

Let me talk to him at the weekend and see what we can come up with.
Sounds like a cool project.
He has a some stainless, but I don't know if there will be any of the length and width needed.
But, I'll see if there is any large enough "scrap" at work too.
My concerns are if there is a formula that could be used to determine tube length per cylinder, to maximise efficiancy. As you will have the hard part of the tubes.
The flanges are just a few measurements, make a Solidworks model, load the program and burn them out.

 

 

In that case, it would be easier to do what Alex did.
Buy the full length headers and fab the rest of the exhaust with aftermarket cats.
I'm begining to think the shorty headers I saw months ago weren't for a D2 after all, even though it said they were. I've found a couple sets when searching, but after reading details, they aren't even for a LR, stupid google.
I really can't belive no company ever made bolt in shortys for a D1 or D2.

 

 

Flanges can be found here:

http://www.headersbyed.com/__buick.htm

I'm willing to bet you can find others, too. You won't find "Land Rover" flanges, but should be able to find Buick 215 flanges. Curious to see where this goes.

 

Also these might work, for much cheaper.

http://www.hellsgatehotrods.com/flanges/exhaust-header-flanges/buick-nailhead-364-425-exhaust-flange/

They don't specifically list the 215, but they're for a Buick Nailhead, which is the same architecture. In theory they should fit.