Hello Javier. I have had a quick read about the GSSR and see that Hett Maylor were bankrupted by problems with subcontractors, the Marquis of Loring being the largest.
I have gone looking for the works numbers 3476 and 3477.
Some images of Sharp Stewart & Company works plates of other locomotives can give an idea of when they were constructed, though works numbers 3476 and 3477 are a lot later than I thought they would be.
1863 - No. 1448 Atlas Works Manchester
1870 - No. 2048 Atlas Works Manchester "
Duke of Normandy" 2-4-0T
http://lightmoor.co.uk/books/archive-issue-47/ARCH47
1873 - No. 2298 Atlas Works Manchester
1876 - No. 2643 Atlas Works Manchester
1880 - No. 2896 Atlas Works Manchester
1889 - No. 3520 Atlas Works Manchester
1894 - No. 4022 Atlas Works Glasgow
1897 - No. 4302 Atlas Works Glasgow
1897 - No. 4322 Atlas Works Glasgow
1900 - No. 4670 Atlas Works Glasgow
1903 - No. 4981 Atlas Works Glasgow
So, your 3476 and 3477 were turned out of Glasgow circa 1888, which would mean Hett Maylor bought new locomotives for the construction (
perhaps they had no other choice with 1668mm gauge). Buying new locomotives cannot have helped their finances with bidding to build the line for a fixed price. The design appears quite old for 1888, though if Sharp Stewart were working to Hett Maylor wanting the most locomotive for the least price they may have cut the specification, with the cab protection being the cost-cutting ("
no need of protection from rain in Almeria mr Stewart!")