My suggested tube set is Nova 29er oversized tubes (37 HT, 38 DT6, 31,7 TT, 31,8 DT), tandem CS, Nova disk brake FB and 19mm SS. Or maybe anybody can advice me manufacturer, who makes oversized tandem steel tubes?
Here, in Europe, I asked Columbus and Dedacciai, and they can't offer anything..
would not hurt to have 36 spokes for a person that weight. Also, I would consider 4130 straight gauge and extra tubes. There are a number of large bikes that have been built for basketball players over the years, you could look at those
Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder
The height at 195cm (about 6' 4.5") isn't too tall and that alone wouldn't be that hard to accommodate. Of course the leg/torso (or seat height/reach) relationship might be rather different in proportion then other more typically shorter riders. You'll have to get a feel for that aspect of the fitting and resulting frame proportions.
I think the weight is more the challenge. I second the use of tandem or disk grade fork blades. I also have a concern about standard steerers being stiff enough. This is where a 1.25" steerer might be a good choice if you could find one (and crown and stem). I would consider a thicker walled steerer (in 1.125") otherwise, including a straight gage CroMoly. I'm not sure what a DT6 tube is... But a 31.8 DT might be a bit skinny. Maybe step up the DT and use a ST that allows a big diameter seat post.
Otherwise pay attention to the tire clearances as the rider will likely want wide and tall rubber, use a 135 rear hub for serviceability, and also pay attention to the weight balance fore and aft. tall riders have a lot more weight over the rear wheel, a longer chainstay might be in order. Andy.
I would wonder whether you couldn't do something simple like 1.25 TT, 1.375-1.5 DT, 3/4" straight for the stays, all .035. I'm sure you can get by with 1.125 head. That is overbuilt for just about everything that it is put on, so for a comuter, no 30 foot drops... Probably fine.
You can throw in a chainstay that is tapered, though it isn't really as efficient as a straight tube in this application. But it makes it look like a bike. A tandem CS is OK, but some of them are like truck axles so be careful which one you order. A stiff touring weight stay is all you need, bumped up a notch.
There are some super heavy tube sets, but all they really do is hover a thou off the straight tube anyway, so you can suit yourself. I find it hard to believe that anyone really knows that a butted tube that is a radom thou thinner is actually working any better. But often the butted is cheaper and doesn't require as much cleaning, so it is easier to use.
OP; Recommend check on Nova Cycles (see builder suppliers section). If you search there using "tandem" as a search string, you will find a nice fork crown, chain stays, etc. Read the notes on using the tandem CS's as xHD fork blades. Quite a few double OS tubes are available also, but be sure you check the lengths to make sure it is long enough. I would think a 1 5/8" down tube would do the trick...or maybe be too big. Of course also check the thickness of the butts and the centers.