Crankwelding is done all the time with great results, especially known in the VW engine arena. Many places will actually hardface the journal areas so if they loose a bearing during a race, they won't have to replace or reqork the crank, just swap the crank to another case and replace a rod or two... And those are 10,000 rpm engine with turbos pumping 45psi + of boost in many cases.
Japanese were making 3.5L L28's in the 80's, and true to form, almost 30 years later someone here with enough time and curiosity has come across standard techniques that got him within 100cc's!
This is standard technology, it just takes application of the techniques to this situation to make it happen.
Five years ago many would have said an L35 DETT would have been impossible as well. Except me, since I've seen one....in 1986!
OH, and BTW, my understanding of the Japanese Build was that it was accomplished using liners. This was not some sedate engine, either! Full 7500rpms of useable engine speed...under boost!
Tony, what kind of VW engines are you reffering to? What head did this L35DETT have? Was it the same car that Alan T. (HS30-H) pictured during his stay in Japan?
I'm wondering about the rod to stroke ratio in the 3,5 litre engines that you mentioned. In a standard LD28 crank / L24 rod combo, r/s ratio is 1,6. A 89mm stroke crank with L28 rods would have 1,46 r/s ratio (a 89mm/89mm bore and stroke should give about 3,3 liters, still less than 3,5). That's not a lot, considering the fact that these engines rev quite high (7500rpms of usable engine speed?), and the forces pressing the piston against the cylinder wall increase by a large margin.
A taller block, such as the LD28 unit, could be a solution for this... Can't wait to see the LD28 block pictures!