Anything and everything that involves swapping a LHD to RHD.
Things like re-routing of the brakes/pedal boxes. Sterring rack. Quality of the interior install.
It depends on how much B&C had to custom fabricate and how much they bought off the shelf from Alfa.
I seem to remember something like the brake servo or clutch cylinders are a massive PITA on RHD in comparison to LHD due to the location of the pedal box - maybe worth searching the forum for?
Im not saying it applies specifically to these GTV conversions but in the past have seen some right horror story conversions on the internet - Ford F150s for example with rubber belts to convert the steering from one side to another etc etc.
-1998 916 Spider 2.0TS Lusso-
H&S Corse stage 1.
CATCAMs stage 1 cams with Savali custom ECU remap.
305mm discs with 166 4-pot callipers.
Ragazzon exhaust mid section.
Biscione Racing 2x70mm rear section.
17" Zender Siena wheels with 3mm rear spacers.
etc etc etc!