The schwimmwagen is a totally different animal to a tank.
I would estimate an absolute minimum of 4 + times the work in a schwimm. Every panel is sheetmetal with compound curves, which require a lot more time and a totally different skill set to the tank build.
If you are sticking with vw running gear building a reasonable approximation of schwimm running gear but in 2wd would be fairly straight forward, reworking 50's parts, but 4wd, ouch.
For 4wd your only option for a swing axle transaxle (like the original) is an original KDF box or a custom reworked 2wd box. Reworking a vw box for 4wd has been done but...
For the rear reduction hubs the bolt on options are KDF or barndoor kombi which are in a similar price range to KDF parts. The 3rd option is vw australia built Country Buggy reduction hubs, but they only made about 2500 of them for the australian and phillipine markets, so they are less common than the others, plus they are based off later kombi parts so are bigger/heavier looking.
The more accessable 55-60? kombi reduction hubs don't bolt to the beetle style trailing arms. To make them bolt on you either need to make an addaptor block which won't look right or weld an addaptor to the redux hub that looks like the original.
If you want to use the original style torsion bar front suspension but 4wd, a later front beam could be modified to look right but for front kingpin carriers and spindles your only option is again original KDF or total custom fabrication. The suspension geometry means the machining cuts are not all parallel/linear/concentric.
I'm not saying it is un-achievable, it is just a massive undertaking.