The information I have is that the designs of the stone wals of the fortification were made by Gaspard Chaussegros de Léry around 1745 and completed around 1752-5.
After 13 sept. 1759, the Brits under Townshend did not fire a single canon shot at it because a) he had too few large canons (the two brought by Wolfe were field canon, which could do, using grapeshot. do human damage, but even with full balls (6 pounders) would barely affect a fortification, and the batteries intended to receive the canons were not finished when on 17 sept. 1759, Québec"s governor De Ramezay, made a surprise offer of capitulation, which was accepted in spite that its main demands were barely acceptable by the Brits.
After tje capitulation of 1759. then the one of 1760, and the Treaty of Paris of 1763, the Brits made a few improvements and changes to the fortification, but as far as I know nothing of major importance . It would not have been worth it, considering they had no serious reason to do so and spend a lot of money that was better spent on preventing a separatist revolution in their original 13 British colonies in America, which started brewing as early as 1763. in which England conceded that the colony of Canada, now renamed province of Québec, as a catholic "papist" colony. It was made worse by the royal proclamation which, among other things, gave, as promised, the Indians the control of the Ohio and the Mississipi valleys, which was what the colonials wanted in the first place and had fought for, now all for naught. English money was more needed to reinforce its army in the 13 colonies than to make improved fortifications for Québec, the city.
As for Lord Dufferin's role, not only do I entirely agree, but just about everybody in Québec, the city and the province, is still grateful to him. He was a visionary man, who at a time when tourism was a new enterprise, a consequence of the growing train industry. he made excellent previsions of what would interest tourists at least a century later. He cannot, and is not portrayed in Québec as a "big bad english", quite the contrary.
I would appreciate any information you could give me which could update this post.