I just paid $35 for a complete BN4 heater, and got it fired up this
evening.  Noisy, initially smoky, and *really* cranks out the heat.  The
temperature control actually won't let the burner stay on very long, and
the thing cycles burning for about 20 seconds, and then just blowing for
about 90 seconds.  After turning it off. it blows until the whole heater
is stone cold.

When finally running, it was very clean burning, but still noisy.  It uses
a lot of electricity -- big blower, glow plug, two electric fuel pumps and
a coil/sparkplug.  If I decide to install this in my Westy, I'll probably
have to modify its behaviour -- blow hot for a bit, shut off the gas, and
blow only until it is safely cooled and most of the residual heat has been
collected.

Unlike the BA6 that came on later buses, this cannot be mounted under the
bus, but the whole heater is much simpler and more compact.  An even more
compact unit is the BA4 heaters that came stock on Type4 VWs (like the 412).
I also paid about $35 each for two of these, and they are identical in
operation to the later BA6 so you can use your Bentley to service it.
These are flat units -- shorter, wider and thinner than the BA6 (and less
powerful).  They need a circulation fan, which the BN4 does not.

I was so thrilled when it finally fired up!  I had to rebuild both fuel pumps
and the relays.  I guess you get what you pay for.  Now if I can figure out
the silly Webasto heater I have.  Nice unit, but pretty confusing right now.
No documents, of course (I traded a BA4 for it).

Malcolm