Stephen's intention in fantasizing that his uncle Richie works for "master Goff and master Shapland Tandy" is obscure, but it seems both disrespectful and distinctly Irish (not an unusual combination). A "goff" is an idiot. Napper Tandy was a hero of the United Irishmen rebellion in the 1790s. The second name may also involve an allusion to Tristram Shandy, hero of the brilliantly digressive novel of that name written by the Irishman Laurence Sterne.
"Goff" is an obsolete English word derived from the Middle French goffe (clumsy, awkward, stupid). The OED quotes uses from the 16th through the 19th centuries, with synonyms like "a foolish clown." Where Stephen may have encountered such a word, and why he should apply it to Goulding's employers—it does not sound much like either Collis or Ward—are questions not easily answered.
Napper Tandy was no foolish clown, but a determined patriot who led troops in the cause of Irish independence. Stephen thinks of him later in Proteus in connection with a song about the revolt of the 1790s, as he remembers meeting another exiled revolutionary, Kevin Egan, in Paris. Perhaps he already has the strains of the tune floating through his mind.
The introduction of "Sh" into the name makes Gifford hear an allusion to Tristram Shandy (1759-67), and the brainy comedy of Sterne's novel is so Joycean in spirit that this inference seems natural, but if an allusion is involved it is hard to know what to make of it. One might observe that Tristram received his name by an unlucky accident: his father thought that names were destiny, and that no name more certainly doomed one to failure than Tristram, but the name he chose for his son, Trismegistus ("thrice-great," after the legendary mystical philosopher Hermes Trismegistus), became garbled into Tristram when the maid miscommunicated it to the priest. One might go on to note that in Finnegans Wake Joyce played happily with Tristan/Tristian/Tristram and its root meaning of "sad." But one would then be forced to admit that this name does not actually appear in Stephen's fantastic coinage . . . "Shapland" is an uncommon English surname, possibly derived from Sheep-land or Chaplain, but it offers little for a reader to work with. What's in a name?