Chris - a reasonably easy solution is to get some longer collimation bolts and springs to move the primary up the tube by the amount you need. I did this to my 200mm skywatcher reflector - no probs. Bunnings sells a fair selection of compression springs - but some of them you may need to cut to size.
Just be aware that if you do this, you will then have problems getting focus with your eyepieces - but this is easily fixed with an extension tube.
It sounds though that your focuser may need upgrading anyway - in which case just get a decent low profile one, and you won't need to move the primary....
Adam