It looks like a combination of code snippets from Carrie's solution, the main solution in this thread and the one in the thread I referred to in my last post has done the trick.
It seems as though the php code in
http://forum.x-cart.com/viewtopic.php?t=19684 has generated the correct results for the template changes suggested by Carrie.
I now have Manufacturers appearing in products.tpl and product_t.tpl whether viewing by categories or by seach results, and also in Featured Products. The code to have Manufacturers appear in product.tpl as suggested in this post also works a treat.
Good news all round - sincere thanks to all the forumistas who have contributed to this one!!
FN