I presume this is referring to 'Q3' which is shown in various QE2 books? Or is it even earlier than that?
Regardless, it would have been a disaster.
An utter disaster.
QE2 was revolutionary, and it was only that, which saved her, when all other "similar" ships had to end their lives (e.g. France and SSUS).
Twice they changed direction - in the right direction - once when ditching Q3 and commissioning Q4, and then again during Q4's construction when they altered the design even more. Q4 (QE2) was always designed to cruise, and was not simply a direct successor to the first two Queens - because that was simply no longer needed or wanted. If they'd built Q3 instead of Q4, Cunard would have gone under in the 60s or very early 70s and would only be a memory now. Q3 would have been laid up and/or scrapped.
One more thing saved QE2 - in a bizarre twist. They deleted her fourth boiler to save some money, but this made her unreliable in service, because there was no redundancy when things went wrong, and it meant the other boilers were over-used, especially as QE2 had a MUCH more demanding turnaround cycle time than the old Queens. So, by the 80s they had to do something to fix her, or scrap her, and she was too good to scrap, so they re-engined her. Had she had the 4th boiler, in my view, she'd have made it in the early to mid 90s I think, but then been too old to re-engine.