Drilling/plugging accurately in masonry.

It wasn't my day yesterday. Not only did my SDS drill start playing up (see another thread I started), but I also had fun and games trying to fix some shelf supports to brick walls.
I am actually in the process of installing a Wickes fitted bedroom. This involves building a frame that runs parallel to the rear wall, and fixing shelf bearers to the rear wall. The shelves then sit on both the frame and bearer, and some are screwed to both to fix the frame in the front-to-back direction.
Anyway my problem is how to drill the holes for the bearers accurately. It is important that they are screwed to the wall at a certain height and ideally at the pre-drilled positions in the bearers. The pre-drilled holes will take a size 10 screw so I planned to use these together with 8mm plugs. There are 3 holes per 50 cm length of shelf bearer.
The first bearer went up fine, and the first hole for the next one was fine, but I could not for the life of me get the other two holes on that bearer lined up with it. In frustration, I ended up using a couple of 6 x 60 hammer-in frame fixings instead but I am worried that these will not be sufficiently strong. (Any opinions?)
So - does anyone have any tips on this? It doesn't seem to matter how accurately I measure the position of the holes, they end up in slightly the wrong positions. I should mention that I have been using a smaller bit to get a pilot hole as this seems to be usually recommended.
I have an idea of something to try that I'd like opinions on. The idea is to create a template out of a batten, with 8mm holes drilled at the required positions, and fix that template to the wall with the 6mm frame fixings (at different positions from the 8mm holes). This is based on my experience that the 6mm fixings are relatively easy to get right. The template would then provide a guide for the drill at the correct positions for the 8mm holes. Does this sound at all reasonable? Has anyone ever tried anything similar?
I'd be really grateful for tips on this - I have a *lot* of shelves to fix yet!
Ian.
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