The only on-line version of the Clydesdale Stud Book I could find is here:-

The Clydesdale Stud Book @ Internet Archive Volume XXVIII, 1906 - a scanned copy of one year's edition of the records of The Clydesdale Horse Society Of Great Britain and Ireland.

The scanning interpolation is pretty poor, so finding the name of a particular horse or owner would be a matter of luck. There are scanned hard-copy versions of most years' editions available as on-demand reprints via Amazon for about £19 a copy ($30?).

Kat, there's a reprint available of the American Clydesdale Stud Book V3 (1887) ($37.19 from Amazon.com with Free Super Saver Shipping!) which might contain details of your grandfather's Clydesdale. There's a warning on most of these reprints about the limitations on quality, so may be as difficult to peruse as the on-line copy. A used original appears to be available at £1,161.91 (+ £2.80 postage, the chisellers). Maybe a typo?

Ross