Re-lace campagnolo G3 wheels?

I've got a pair of early noughties Zondas which run beautifully but the rear rim is getting a bit concave so I'm thinking of a rebuild. Campy rims are expensive, if you can find one, however Shimano do a 21h 30mm rim for the WH-RS330 which can be had for £30.
The question is, has anyone relaced a G3 rear hub to a regularly drilled rim? Is it even possible? I'm guessing I may have to source some different length straight pull spokes for the drive side but the NDS is radial so should be fine given the rim depth is more or less the same.
Any thoughts/advice appreciated, I've found nothing on the web...

It can be done but you'll end up with spacing more like a Fulcrum wheel than a G3.

You'll need a 28H, use all the gear side and miss alternate holes on the NGS.

You'll need a deep rim - to control the radial true - even then, it won't be perfect. Campag G3 rims are not perfectly round out of the box, they are very slightly heptagonal so that when the correct tension is pulled onto the spoke groups, they pull into round - using a 3rd party rim you won't have that option so the only thing that you can do is use a deep rim to get as much radial rigidity as you can. Dialling the spoke tensions down is not an option with only 21 spokes - you need to be at 130 - 150 kgs on the gear side, probably. Depends on your weight and the intended purpose, whether you are running tubes, tubular or tubeless ...

Because you are dealing with high spoke tensions, the spoke length needs to be pretty much spot on - so you are almost certainly into recalculating spoke lengths. On the gear side you have to bear in mind that the spoke exit angles from the hub are made for a G3 rim - building straight pull onto a rim with different spoke spacing might end in tears. Depends on rim depth for good entry angles at the rim, too.

If the rim's too deep, the entry angles will cause you grief as the nipple may not be able to turn enough to align well - too shallow and you'll potentially struggle with roundness.

Don't take this the wrong way - but to do this and do it well, is not a job for a rookie wheel-builder - by which I mean, it's not a job for your 1st wheel, or probably even your 21st ... as a job, to get it right, you need a bit of experience to choose the right rim, the right spokes, and I'd advise an accurate tensiometer (not the Park one).

Even using the right parts, most shop wheel-builders send the wheels to us to be done.

We stock virtually all of the Campagonolo rims that are still available and have one or two that aren't ... but you are right - relatively they are expensive. The ones that we don't have we can order from the factory - if they are in stock in Italy, delivery is around a week to three weeks,it depends where you catch us in our order cycle.

I say it myself - but after 10 years as Campag's head mech in the UK, I've probably built more G3 wheels and adaptations of G3 wheels than anyone else in the UK (upwards of 200) and I am still learning new tricks ..!

Thanks for such an informative reply, I thought it might be a bit fiddly but not this bad!

Interesting point about a 28h rim, I'd not thought of that but it makes sense.
I guess roundness is a challenge because of the large areas of unsupported rim in between the triplets but the hub exit angles are in conflict with a more even spacing to address this?