The pronunciations recorded by SGDS in these areas can be represented by the spellings cnachp and tachpaidh.
SGDS, Vol 3: Item 360 shows that the final vowel in this word is dropped in all of Perthshire (apart from that part of the county lying between Ben Lawers and Tyndrum), Aberdeenshire, Inverness-shire (east of a line running from Laggan to Inverness), Morayshire, Nairnshire, the Black Isle, Easter Ross, Caithness and Sutherland (excluding Assynt).
The regular dropping of the -adh ending is a feature which is found in a very restricted area of the Highlands: SGDS, Vol 2: Item 133 shows that the -adh ending in the verbal noun a' bualadh is dropped in Strathspey, Aberdeenshire and in most of Perthshire (apart from the Tyndrum and Rannoch areas).
SGDS obtained the form an zaoghal (for an saoghal) in Strathspey, Nairnshire and Perthshire, and also in the Cowal, Minard, Inveraray and Dalmally areas of Argyll (Vol 5: Item 738).
This feature seems to have a fairly similar distribution pattern to that for the eclipsis of 'broad s', but again we cannot be sure of the full geographical distribution of this feature, for the SGDS researchers seem to have asked some informants for the pronunciation of the adverb an seo 'here', while asking others for the pronunciation of the determiner seo 'this' (SGDS, Vol 5: Item 753).
SGDS Vol 3: Item 384, using the test phrase gum faiceadh records the form gum vaiceadh in mainland Argyll (between Knapdale and Appin), throughout Perthshire as well as in Aberdeenshire.