I have a Jones on demo with a view to buying, currently set up half fat. At some point I would like to get a 29 front wheel for it. Given that.I need to get a Jones/whub/CK hub to build it up I was thinking about trying a fork and wheel I have in the workshop in the short term, assuming I buy it. It would be about 5mm longer than the Jones fork and the trail would be 45mm rather than 55mm.
What sort of difference would the -10mm trail make?

fwiw I have a Jones and a spare fork about 7mm longer with 45mm offset in the garage. I reckon the Jones would feel crap with it fitted, you'll add a fair bit of trail and make it feel sloppier with a shorter front-centre, it's already about as short as an MTB could go and rides well for it - suprisingly. It would also be a lot twangier with a normal fork and lose that rock solid fell that makes the Jones F+F feel so good.

And Jeff would frown if he saw it : )

Cheers James, just a thought. Obviously I wasn't going to post pictures were Jeff would see them :)
Just as a thought, do you think there is a lot to be gained from having a truss fork? Like the idea, not sure if the reality is noticeable for a rider such as me(pretty pedestrian!). That and they're expensive or pretty rare used.

I tried the bothy bikes Jones with the truss fork a few years ago. still remember how stiff it was without feeling harsh

I've not ridden the unicrown fork so can't compare. They're said to be a little less stiff than a truss but they'll surely be stiffer than a standard fork and the 135mm hub is a big part of the front end ride feel anyway. And don't let my comments put you off trying it, I don't think it'll give a good impression of the bike but who knows : )

It was just a thought as I say, the plan is to build a 29/25 or 35mm wheel for it. Have to say how impressed I am with the ride; balanced, comfortable yet surprisingly nimble on steepish terrain. Thanks again for the input.