Bigger brake kit means at least 15", most likely 16" wheels to clear the calipers on any of the high quality kits; Small Car, GoWesty, Van-Cafe, etc. Also, with the 16" steel wheels, you will also need to add 10-12mm spacers for clearance. These 10mm spacers will then require new longer lug bolts to allow proper engagement. Alternately you could opt for alloys, although they are 7" wide, a bit much for a 205R65-16 tire. However that is all that is available, at least easily found.
The wheel/tire packages sold by the the same parts vendors will clear the brake kits just fine, but are pricey, $1K to $1.2K. I sue the Nokian van tire, 205R65-16 or 215R65-16, the latter size will not fit in my spare tire area up front, the 205 will, with some mods, and only on a steel wheel (narrower). The 16" alloys with either tire will require an external spare tire rack, due to the width & diameter, at least on my van. 
But you'll have nice brakes...
Jon
 
> On 5/17/2015 5:34 PM, Neil N wrote:
> Hi all.
> 
> The back ground info is below, but here's the bottom line; I need to
> improve the braking on my '81 Westy. I suspect the rebuilt calipers I installed
> several years ago, never worked 100% correctly due to poor quality assembly or
> parts. i.e. one leaked right away. Image: http://tinyurl.com/lqsx4gf
> 
> My choices:
> 
> - upgrade steering knuckles, install a "Bigger Brake Kit"
> - upgrade steering knuckles, install new '86 + calipers etc.
> - rebuild a spare set of Girling calipers.
> 
> Is rebuilding the old style calipers a waste of time? Most of those
> cores are pretty old now,
> have likely been rebuilt at least a few times, and I've heard that
> some rebuild kits may not be of good quality. However. I have what may
> be a decent set of calipers I could clean up and rebuild.
> 
> Thanks,
> 
> Neil.
> 
> Since I'd been driving my '88 Westy the last while, I've since
> discovered that the brakes in my '81 Westy pale terribly in
> comparison. I had a Vanagon mechanic road test the '81 brakes. His
> first comment about them was something akin to 'they're crappy'.
> He also suggested it could be a caliper issue; I'd installed rebuilt calipers
> several years ago (along with doing a bunch of other brake work)
> The brake system is in otherwise good condition but the brakes just
> don't "bite" as well as my '88 brakes, there is considerable fade,
> pedal doesn't feel as hard as that on my '88.
> Rear shoe were is normal and even. I'm certain no air is in the
> hydraulic system.
> The mechanic said he'd run into a problem like this before. He removed the pads,
> and carefully pushed the brake pedal down to move the pistons further out in an
> effort to (reseat?) the piston O ring. He said this improved the
> brakes and that the
> issue had to do with either the piston position or the O ring itself
> (not flexing enough?)
> 
> --
> Neil n
> 
> Blog: Vanagons, Westfalia, general <http://tubaneil.blogspot.ca>
> 
> 1988 Westy Images <https://picasaweb.google.com/musomuso/New1988Westy>
> 
> 1981 Westfalia "Jaco" Images, technical <http://tubaneil.googlepages.com/>
> 
> Vanagon-Bus VAG Gas Engine Swap Group <http://tinyurl.com/khalbay>