Despite being told by a machining place that it aint, In fact it IS possible.
bore x stroke
2.5 81.6mm x 79.6mm
3.0 86mm x 85mm
do the sums and you'll find that you'll lose 2.2mm of wall thickness and as the walls are very thick (12-14mm) to start with.
It's looking like £200 for the rebore, and I got a rough quote of £10/piston for pocketing.
Having both cranks is nice, in that I could use the 2.5 crank, and have a higher revlimit and less grunt, or use the std 3.0 one. decisions decisions decisions.
Oh, and has anyone got experience of (and prices for) acid dipping blocks and heads to remove limescale? I was quoted £20/head and £40/block, and this seemed a bit high!