the indicators that you use to tell that the numbers have been altered.
Someone in the market for a Gold Star should be very
worried by this set of cases. It is the best job I've seen to date of forging a new set of numbers. The font he used is all but indistinguishable from the correct GS front, the layout of the letters, numbers, and 'dots' is correct, and the reprofiling and retexturing of the surface under the stamps extends far enough so as not to be obvious except by very close inspection. However, our first clue that something is fishy is the number itself, 8259, which is approximately 1000 higher than that of the last Gold Star made.
There is another set of numbers on the front lug that distinguishes a GS from a B31 (not shown on the eBay
listing), but since the forger has the correct stamps those could have been altered as well. However, one set of numbers he didn't alter, that gives the plot away for these cases, is the date '17 7 52' you can see stamped inside the timing cover showing these cases were made four years before the DBD made its debut. With this in mind look at the 2:00 position on the drive side case and you can see where the hole for the oil return line was filled in. Even if this was a Gold Star case that hole disappeared with the 5000-series ZB, and the vestigial boss in the casting at that position was eliminated with the CB.
The listing says "The cases are converted B31 but are indistinguishable"
from Gold Star cases. Unfortunately, while that is nearly true for the external
appearance of these particular cases, the internals are a different matter. Among other differences, Gold Star cases benefitted from additional strengthening ribs on the inside of the cases that aren't present in non-GS engines.
Of course, anyone who buys the upcoming next edition of 'The Gold Star Buyer's Companion' would have the information and photographs required to identify all of these features for themselves and would save themselves potential heartbreak and thousands of dollars/pounds/euros by not buying a "Gold Star" having forged cases.