Thank you Steve for your encouragement.
Unfortunately, I'm a really poor welder, and very afraid of damaging the bodies. I made a test yesterday evening (not with Durafix, but an equivalent melting @ 380 °C) on small aluminium sheets : works great, but when I tried with the carb, I wasn't able to build enough heat to melt the stick by touching the body, and didn't insist - fear of seeing the body collapse locally...
Maybe I use the wrong type of tool, because I only have a very small oxyacetylene torch - too high a risk of burning a hole with it ?
If I can't manage the welding job, the last - yet not the smartest - solution would be to screw in plugs...
Another topic now : having noticed the throttle shaft play in the body, I intended to replace them, but as you guessed before the bores are worn out, so there's a play even with the new shaft... I thought that shafts in the SU kits where oversized : in fact, they appear to be nominal, but are supplied with new bearings to insert. Having no machining tool, I need to find a workshop to do it - really don't want to screw everything up...
The road is long, long...
Matt