Craftmanship to create these kind of modification certainly very impressive - anyone who has seen Allen Millyard's videos would see how much detailed machining/welding work is involved. However, whilst inline 8 cylinder engines are theoretically capable of perfect primary and secondary balance if firing order is optimised, these are not used in practice due to inherent torsional vibration issues that cause fatigue cracking and crank failure. It should be possible to add harmonic viration dampers (as most inline sixes do as well) but the calculations required to specify these are quite complex and would probably require expensive software. Adding these to the end of the crank would make the engine even wider.
Just a thought but still appreciate the conversion work involved.