I used the original airbox and trunking on my 32/34DTML carb and never had any problems with carb icing. It seems those running pan filters do have issues with icing, especially around this time of year. If I was doing a Weber conversion again I'd still stick with the OEM inlet, with the cold air diverter valve intact - it's not doing any damage to the performance, after all.
I've no idea about your fancy gaskets, but you just need something that fits and seals to be honest.