Hi falo,
The problem with the /42 specs is it is bigger in all dimensions, IIRC around 1.2m in length and 0.4m in beam and height, the length in 1:72 would be relatively easy to solve by adding a total of 16.6mm in one or more sections, for accuracy you would need to add around 5.5mm to the beam, not so easy, as this in design was an increase in the pressure hull's diameter, although at 2.75mm each side you enter my argument for building a IXC/40 fom the Revell U 505, unless you vernier it you would not notice. The tower would be of the term IV style, both periscopes were to be in the tower rather than one in the control room, as the VIIs had up until then, but I don't think that you would need to use the U 505's tower as that would need a change to the pressure hull tower rather than the external term design. The other major changes would be the lower platform AA weaponry. Originally designed with 2cm quad vierling, it would have probably been upgraded to a single or twin 3.7cm M42 or M43 and the radar/radar detection equipment would need to be upgraded.
The cheats way, (no such thing in modelling) in my mind would be to choose a type VIIc model in a smaller scale, (1:350/1.400, maybe even the Revell 1:144 VIIC/41, which I know is over sized in length, never measured the models beam and not at home right now) which is already overscale in it's beam.
To quote a former president - we choose to do these things, not because they are easy, but because they are hard.
Regards,
Jon