The locomotives are described as "available," meaning (to my mind, anyway) that they were available upon issuance of, and acceptance of, specification and bid in contract with a customer. There was in all likelihood nothing in the design of these locomotives not already built for road service, including the trucks and carbody design. The major alteration was the inclusion of a turbocharged instead of normally aspirated engine. (Of course, the main generator would have changed from the 480 model used on the 2000 HP units to the 489 as was found in Seaboard 4500, and other early units with turbocharged eight-cylinder engines, or else the 471.) So it's safe to say that no additional design work beyond what had already been built would have been required.
Getting back to the original intent of this thread, though, it seems significant to point out that what might have been a design path taken by any exercise at EMD to equip an E-unit with 3000 HP at that time was not pursued when actually offered by Baldwin. These would have had more weight on drivers, in a pair, than a single equivalent Centipede - roughly 520,000 lbs for the two A1A-A1A units against 410,000 lbs for a single Centipede. Their adhesion in freight service would have been improved, clearly - but no road bought Centipedes for what we might think of as conventional heavy freight service, since PRR bought its units as passenger locomotives and SAL and NdeM used their units on lines with low axle load limits. From a mechanical officer's standpoint the 3000 HP A1A-A1A unit would have been better than the Centipede, it looks to me - and still the railroads plowed forward with what we think of today as wholly conventional road freight locomotives, with the F-M Erie being the sole exception. It might be oversimplification to say that tractive effort ruled the day, as train speeds still remained low compared to what we think of today, but it's probably quite accurate.
I believe it's exploring the relationships such as this which get at the heart of why EMD would never have bothered to try to offer any such dual engined 3000 HP locomotive -- especially more if one considers Kirkland's quotes of Dilworth on negative qualities of the Centipede.
A much more fun idea I think would be a kitbash to depict an E-8 or E-9 repowered with two 1500 HP 12-645E engines and D77 traction motors. Maybe even give it AC drive for full parallel motor operation at all times, and IDAC wheel slip control. But that's the extent of my speculating tonight!
PS Yes, Allen, I'll dig around for more K-M info!