18 Mudgee / 81 Young
In the 3R16 device, the position of the numerals relative to the rays is the giveaway.19 Rylstone / 61 Gresford
The 2R and 3R types are both illustrated below. The 3R type speaks for itself, but in the 2R type, the rays are closer to the numerals in th 61 device.
68 Scone / 89 Kempsey
Not the easiest to pick apart, but this will only be a problem if you have both on DLR or diadem stamps. Scone had a barred numeral before the DLR stamps were superseded.161 Aberdeen / 191 Windeyer
I believe these are the hardest to pick apart. Strikes of Aberdeen are usually pretty nice, and also rated common.
For other numerals, different device types were used at different offices, so it's easy to pick one from the other.
Three other instances are worth mentioning.
18 Mudgee / 81 Warwick: The 2R type has 17 rays in the former and 20 in the latter. The bottom loop of the 8 in the Mudgee device is wider than the top loop. Warwick is a Queensland office, and any examples of the numeral on a perforated 6d or 1/- diadem, if they exist, will be of the greatest rarity.
69 Murrurundi / 96 Maryborough: The numbers in the latter (20 rays) are further apart than those in the former (21 rays). Maryborough is also a Queensland office, so the note for Warwick applies here too.
618 Telegraph Point / 819 Yarras: In the latter, the numbers are larger and further apart than the former.
Lastly, the type 5 devices for 18 Mudgee and 81 Young can be determined by the shape of the 8. In the Mudgee device, the bottom loop is bigger than the top loop. For the Young device, the loops are almost the same size.