Richard
Trying to get in quick before Alien gets here and monopolises the sandbag! You dont actually HAVE to have the radios in to run the intercom and in any event you dont need two 353's as this would be quite unusual. You will need either an IB2 or IB3, a commanders box and probably a couple of crew boxes, together with a 2 pin power lead, which goes to your IB 2/3. You then need the leads to put the boxes into the harness (12 pin i think) and obviously your headsets and pressels. If you get the yellow faced ANR boxes you need to make sure you get compatible headsets and pressels. The pressels should be green rather than black. I only have experience of the ANR boxes but I am told they are better than non ANR. As already stated though your best bet is to get some of the literature, have a read, and start by getting the basic intercom up and working, which can be done fairly cheaply, then you can add to it as you wish. As is my way I bought loads of everything without knowing what i needed and now have millions of cables and boxes, but inevitably not what i actually need and have become overfaced by the whole thing and put it on the backburner til I get my gearbox leak sorted.!
Cheers
Tim