Short answers, pulled from the story.
The Football World Championship was an informal series of exhibition matches between the English and Scottish club champions, played on an irregular basis from 1876 into the early 1900s. It had no fixed rules, no governing body, and went by several names including the Championship of the United Kingdom and the International Club Championship.
Renton won the most celebrated match of the series, defeating West Bromwich Albion 4-1 in May 1888 at the second Hampden Park in Glasgow during a thunderstorm. Renton's players all came from their small community in Dunbartonshire, while West Brom fielded only English players, giving the fixture a genuinely international character.
One small pewter trophy was commissioned following Renton's 1888 victory and is today held at the Scottish Football Museum. It is the only known physical prize from any match in the entire series. A 'Champions of the World' sign was also erected at Renton's Tontine Park ground, but it did not survive the ground's demolition in the 1920s.
On the 27th of April 1895, Sunderland met Heart of Midlothian in Edinburgh in a match billed locally as the championship of the world. Sunderland, then known as the Team of all Talents and formed almost entirely of Scottish players, won 5-3. The Sunderland Daily Echo acknowledged it was an important event because both clubs were the respective league champions of England and Scotland.
The last recorded match in the series was played between Bury and Rangers across two fixtures on Christmas Day 1903 and the 4th of January 1904, with Bury winning both 2-1. By that point league calendars had expanded and leading clubs were touring Europe, making an exclusively British 'world' championship no longer credible.
The 1886-87 FA Cup was the last edition in which Scottish clubs competed, with Rangers reaching the semi-finals that year. After Scottish clubs withdrew from the FA Cup, cross-border competition at an official level ended, which actually increased press attention on the informal championship matches as the remaining arena for English versus Scottish club rivalry.