Hi Fiona,
sorry I've been slow following up on this. To cut a long story short, work intervened.
I've got a combination of local knowledge (grew up near Eaglesham, interest in Pollokshaws, trained in Greenock) and a reasonable library.
Though I was caught out (I now know) by Small's UP book. It's available for download, if you have broadband, at [
http://www.archive.org/search.php?query=subject:%22United%20Presbyterian%20Church%22 ] (make sure you get it all in the window).
The page references I gave you were pretty well duff though. Turns out what you need is volume 1 page 600, and volume 2 pages 171 and 274 (at least - that's what jumps up on a text search).
However, it seems incomplete and I wonder if technically its the Free church one you need for Clement. Small tries quite hard to play him down as a radical that tried hard, got sick and moved on in the direction of Pollokshaws where he quietly faded out.
But then, Andrew McCallum's history of Pollokshaws (Pollokshaws : Village & Burgh : 1600-1912) at pages 84-85 reveals a lot more more, including that Clement's selection as minister at Pollokshaws was strongly opposed (though obviously he won) and that this helped split the church again. No genealogical data in it, but it must be good to have such interesting ancestors and this must be worth another, more insistent, trip to the Mitchell...