Hello Graeme,
Short answers are, pulled the tube astern and the tube (from memory) was approx15 inches long. When the time comes, it will need to be measured and cut to length.
The critical points are:
1. That the copper tube is a tight fit into the fibreglass tube ie no slop.
2. That the radiator hose (that supports the gland/seal) on the inboard side is effectively clamped whether that be onto the fibreglass moulding or the copper tube.
You are on the right track. Give the pulling idea a go, if it doesn't work then it's out with the recip saw and mini chisel!!
Keep in touch,
Cheers,
Maurice.