Yes, I think the 8/2 is problematic as well, although I hasten to add I've not yet read the numismatic circular in which MG espouses the theory.
The idea of 8/2 may be flawed because, as you say, no 2's had been used since 1827. Bramah, at pages 104 - 105, does mention the fact that according to the 1852 parliamentary return of the Mint that year, 236,424 pennies were struck, but none were ever seen. The Mint authorities "can only conjecture that they were all brought in again to be melted, but were they ever issued?" (Montagu). Or were they all struck from the previous year's dies. That sounds the more realistic scenario, since, as Bramah rightly speculates, even if only a very limited number of 1852's got out into circulation, at least a few would have turned up and been retained by collectors. As per 1952 and 1954, with one each. Although it is possible that if they were dated 1852, every single one was accounted for and melted.
Conversely, the figure three would have been readily available, and in different sizes as per the ones used in 1853. We know that overstrikes of 8/7, and 8/6 also occurred, so by logical extension, it makes sense that 8/3 was also used - all using dies from the 1850's.
Not presuming to be so arrogant as to say I'm right, far from it. At the end of the day Gouby has many orders of magnitude more numismatic knowledge and experience than I have (or ever will), but it doesn't do any harm to play Devil's advocate and start asking awkward questions now and again.
Finally, what the heck is a Bramah 25c? Sounds like an over something, over something else !!