Pete Brock is looking at this from the wrong end of a telescope. As usual.
The British economy was in the tank when Kas Kasner was trying to get Triumph to spend money it didn't have on new car designs.
The Conservative government had artificially kept the Pound Sterling value high while trying to get a better conversion ratio against the European currencies as it was negotiating entry into the EU (nee EEC). This had killed the export markets for British goods, especially to the USA. The export of British sports cars suffered so Triumph was in dire straits financially. The lack of sales resulted in massive employee layoffs followed by serial strikes and a general election won by the Socialist Labour Party.
The US had no interest in Britain joining the EU and was manipulating bank rates to reduce the value of the Pound by dumping Sterling in the finacial market. Additionally it was not in favor of supporting a Socialist government in Britain and had the CIA playing dirty tricks against Harold Wilson, the Prime Minister, to the point he resigned after being undermined by their accusations that he was a Russian asset. The US also ensured that the IMF and World Bank refused loans requested by Britain to reinvigorate the British economy. So Triumph was just struggling to survive.
If Pete and Kas had paid any attention to events outside their very narrow perspective they would have understood and not bothered to build the TR250.
The design of the TR7/8 had nothing to do with the style of the TR250, pretty though it may be. The late arrival of the TR8, the British sports car that would have best replaced the TR6 as early as 1976, was delayed because of US regulations that implied that convertibles would not be saleable in America for safety reasons plus the advent of ever more restrictive emissions regulations just added more costs at a time when British car companies could not afford the investment.
The TR7's reputation was almost completely ruined by British government interference, forcing manufacturers to locate new expensive factories in areas with little or no manufacturing skills. Then, just to make things worse, the high pound, low dollar ratio meant exports were impossible.
The British government, aided by the CIA and MI5, planted people in the British unions to create problems so many strikes ensued, which was what the by then Conservative government wanted. The fields around the factories were full of (20,000) unsold cars that could not be sold overseas due to their poor price competitiveness. The overnment didn't need more car production. The British worker strikes took the blame for the effects of UK and US government policies in their mutually exclusive plots for the UK to enter the EU and the US to keep the UK out of the EU.
I love reading how the US is whining about foreign intervention in domestic politics when they have been doing that all around the world since WWII. Yea reap what yea sow. Eat it.