8 and 9 speed indexing compatibility

I would like to run a certain gearing combo, and cannot get consensus on whether this would work or not. Basically I would like to use 8 speeds of 9 within this set up, what I'd like to achieve is an old school bike which has a lightweight large gear range, which can be set up to either use the top 8 or the bottom 8 depending if I'm in the hills or racing in flatter country.

Dura ace 7400 8sp STI shifters
Dura ace 7403 8sp rear mech
Dura ace 7410 52/40 chainset
Dura ace 7700 9sp 12-27 cassette
KMC X9SL chain

Will the 8sp indexing work over a 9 speed cassette even though a 9 speed cassette has inter cog spacing of 2.7mm as opposed to 3mm for the 8sp?

Cheers,

It's also really hard to get a hold of a lightweight 8 speed cassette, and I'd prefer dura ace. the 8 speed dura ace ones didnt have the titanium lower cogs, and weren't as ramped and profiled as the 7700 one. 9 speed chains are also much lighter and apparently shift much more readily due to the space avialble for the outer link plate profiling

Moans about a cassette not having titanium lower cogs but it willing to carry 9 cogs (of whatever material) everywhere but only ever use 8 of them.

Go figure.

Edit: To run a 9 speed cassette and alternate between using the top 8 and bottom 8 with an 8 speed shifter you will need to adjust cable tension and high/low limt screws everytime you change the gearing. You will need to entirely reindex the gears to go from 'mountain gearing' to 'racing gearing'. And remember that you'll be re-indexing gears that won't index properly anyway because of the different cog spacing between 8 and 9 speed.

Will the 9 speed chain work ok with the jockey wheels in the 8 speed mech?