try my site for a cartobibliograhy
the most detailed at that period was Smythe's 1826 - a little better than 1inch to mile

There were Tithe plans in late 1830's + 1840's of individual estates - these are on microfilm at Manx Museum - they are at various very large scales but show individual landholdings
A later set of plans were done in 1860's for Lunatic Asylum rate - formed basis of Woods Atlas - then in 1868 came Ordnance Survey.