ABH and ABZ engines.

Faced with being engineless again, I'd like to investigate whether the top end of these 2 engine variants are interchangeable. One reason for this being the relative lack of Audi V8s originally in the UK, compared to A8. So good engines are hard to source.

ABZ engine has been fitted to a 'V8' chassis, but how do you accommodate the coil pack/distributor-less ignition?
There's a number of components common between the 2 engines. I wonder if this goes far enough to make it possible to swap major parts about.

options-
Option 1. A full rebuild of the current engine. My concern with this is that I do not know at this stage where the problem lies.

Option 2. Will the heads from ABH fit ABZ? Then, a good bottom end from ABH could be mated toABH heads, and retain original ignition/ECU/EFi

Option 3. ABZ complete swap, including electronics. Having just stripped a V8, including removing wiring harnesses, this is something I would rather not contemplate just yet.

Option 4. Install ABZ, and convert/modify current electronics.

any advice, knowledge gratefully received. If anyone knows of information in the german language section, this could be translated to assist.

85 WR quattro
90 V8 Silver, 91 V8 Black, 93 V8 Lago
93 100e quattro V6. Titan, i think