Both of my experiences with Weber DGV's have been negative. As a result, I intend to install a pair of HIF6's on my 144s (B20). I have been thinking that I would like to install the HIF6's using a HS6 manifold rather than the goofy manifold that they originally rode on. (The one that was integrated with the exhaust manifold and had secondary throtle valves) Can anyone think of any reason this wouldn't work or reasons why I should stick with the original manifold?

I've used them both ways and not seen much difference unless you have the
FI Head which has bigger ports. Even then the difference is pretty small.
(and you have to port the aluminum manifold to the ID of the ports to get
any real flow improvement. They tell me it is about 13%.)
There are 2 basic reasons to stick with the manifold you've got:
1. You've already got it. No searching, shipping, surprises when it shows
up (unknown condition, etc).
2. (depending on where you live) Winter driveability. The combined manifold
operates smoothly much quicker after startup than the aluminum one. Remember
that the vaporization of gasoline further cools the mixture, making it harder
to ignite. On the other hand, at high speeds, the mixture is in the manifold
for such a short time that it doesn't seem to affect performance much, if any
at all. Unless you are SURE the secondary butterflies are opening fully, you
should take them out (like the other guys said) and plug the holes. On my
first one I used sawed off 5/16" bolts (unthreaded shank) and stuck them in
with permatex. Worked fine.
--
George Downs Bartlesville, Heart of the USA!

It will work very well. I find that the integrated iron manifolds without the secondary throttle plates are by far the best, but the earlier B18 aluminum intake and the FI exhaust manifold work well too, if the ambient temperatures are high enough. In Canada, the iron manifolds work best.
You can also just pull the secondary throttle shafts and plug the holes, but the manifolds don't look as good as the earlier ones.

I agree with Rhys, the Late B18/Early B20 intergated manifold is fine, just make sure you use plastic spacers between the carbs & manifolds & the correct heatshields. The only time I have used the Aluminium intake is with HS8's & 4-1 headers.

The long insulator block spacers are very nice... keeps the heat out of the carb bodies very well and gives you a little more intake length (no, still not quite "tuned" but seems to work better).

HIF44 carbs are reputed to give even more flow (the "metric" version).

Dunno if Rhys offers them as a set, however. I don't think they came stock on anything (I've been wrong before... maybe in Switzerland?) so the linkages would have to come off a HIF6 anyway... unless you know exactly what you need and how to order it from the various gurus (Rhys) or Burlen Fuel Systems.

Never in my life had the SUs "ice-up" but I don't live in Canada. Seems that the argument for icing is the same as the argument for excess heat transfer to the carbs but one ignores the effect of the other (depending on what you are arguing for)... I'm unconvinced. The longer residence time in the manifold at idle is probably good but the effect is largely lost at anything other than an idle.

--
Mike!