Hi Andrew, please take Cristians advice about reducing the secondary size by using a lower profile focusser and positioning the eyepiece closer to the secondary. You do this by using the smallest practical diameter tube for your scope, and position the secondary as far away from the primary mirror as possible. Use the previous advice of others about tube diameter, etc, and run some numbers through the Newt program till you feel comfortable and understand what is happening.
As Cristian said, you have to weigh up the cost of all this, ie. a low profile focusser, a 54mm diagonal cost.
I got my 54mm from Chi Qin Co in Sydney, and they advertise in the back of most Australian Astronomy magazines. Alternatively, you could try Claude at Astronomy Electronics Centre in Cleve, SA. Both carry good quality pyrex secondary mirrors with enhanced coatings and overcoated with SiO or quartz. Probably cost close to $100 though.
Always glad to help a fellow astronomer!
Feel free to ask more questions anytime,
Cheers
Nick