I might be able to dust off my fan calculator at some point but you'll probably have to remind me in early May - lots on at the moment.  You may want some more blades to absorb 70 hp at a reasonable tip speed. 10 mm tip clearance is fine for a cruiser makes 2% difference to thrust but 100% difference to fan safety!

Sounds great Jon. Should be fun!

its all brand new stuff, came with the craft. one of the reasons it was such a bargain.

looks like fresh out the factory. its defo not years and years old, not a spec of dust on the open box.

Just a note of caution to consider is that the fan blades are perhaps of unknown age, and storage conditions and at 70 BHP will be subjected to very considerable forces. I have in my loft similar aged fan blades and hubs, but fear those cannot be ever used with safety. As ever it's a risk/gain ratio question. Large chord blades will certainly reduce noise. 
IMHO

with this old craft i got, it came with a 1250mm thrust duct

3off 6W blades in a 6 bladed hub.

these blades are massive, like shovels.

is that setup going to be any good for thrust?

i have pulleys too, i will work out the ratio tomorrow.

i want to use 70hp @ 6000 rpm