post up how you get on mate as I am sure it will be useful info now and in the future to other futura owners!
Also I almost bought a 2nd hand futura mkII once but didn't for various reasons, one being the speed tubes both had holes in and the seller came back to me saying this company... https://www.aerosafe.co.uk/cgi-bin/s...ml%23a314#a314
quoted him about £100 each for a new speed tubes.
Also this company does zodiac spares... IBS Boat Supplies » Spares Enquiry
Might be worth sending a quick email to both for a quote, may be cheaper than your were first quoted?! Thought I'd say.