I believe that type 3 spindles are different than type 1, but am not sure. I do know the beam is different. Does it bolt in like a type 1? If it doesn' you wouldn't be able to adjust the caster easily with shims like in a bug/ghia (you'd be cutting out a small pie piece and rewelding the frame head). As for how the spindles are different- don't know details, as I don't think I've ever seen a type 3 spindle up close. I've never heard of type 3 drop spindles and am fairly up in what's going on in the VW world, but that doesn't mean they don't exist. I have seen type 3's in Hot VW's with type 1 beams transplanted in but they didn't go into any of the details- I'm guessing they cut off the stock frame head and mount the type 1 piece. Best bet is to start phoning- get the latest copy of Hot VW's and start making the rounds. And I get why you want to go this way- drop spindles do give a better ride.
Sorry I'm not more helpful. Al