Well, thanx to all that chipped in. Being an awful, wet foggy day, I went ahead and tried the 26" fork idea on my existing 29er. I took the relevant measurments suggested both before and after the change as best I could. Interestingly, none of them changed by more than 10mm and the angle of the head set / forks / front wheel was not measurably different. I think this may have been because the "better" forks, having more travel, were longer then the forks I removed, compensating for the smaller wheel. By 3pm, it had at least stopped raining, so I took it out for a very short spin along a local track that I use for "testing" new ideas. The ride involves about 3/4mile on roads, then 1-1/2miles off road on a mixture of hardpack, grass, a little gravel section and since a bulldozer has been employed to get rid of a section of hedge, deep mud ! The bike felt no different on the road section, other than feeling much more "action" at the front end, but none of the twitchiness that was suggested may be felt. Once hitting the hardpack, I found it to be very slick on the surface, but was soon confident in the bike to up the anti and start pushing things. I went back to the start of the hardpack and firmed up the spring action, and then did the same again. Starting from the begining, I was pushing from the first turn of the pedals. It felt great, tracking the ground without any handling issues, onto the grass, then the gravel then the mud. The bike was markedly better with these replacement forks, without any of the possible problems showing up. Of course there is alot more testing to do, but by this time, I looked like the abonomable mud man, and the wife was due home, so a quick hose down for me and the bike, and a cuppa waiting for her ladyship when she got home. But all in all, I'm well pleased with todays efforts.
forkryingoutloud 
Just to finish my contribution to this thread, I have now completed over 100 miles on the new set up of 29er rear and 26er front. The most noticable change in my bike is that the quality of the fork, allowing me to feel much more confident in pushing the boundries when 'off road'. The quality improvement of the forks action, all be it still a sub £100 set of SR Suntour XCR, coil spring and pnuematic lock facility, over the origonal fork is well worth the effort involved in the change over. I'm not totally convinced that it hasnt caused ANY downside. At speeds over 25mph while on road, there does seem to be a certain twitchy feeling to the steering that I had never noticed before. However, that is the only thing I have noticed that could be deemed to be a drawback. And to be fair, its not often that I can achieve that sort of speed. So, all in all, I think that this has been an unmitigated success. As my old dad used to tell me, "if you dont try, you can never succeed" and I think that this could be seen as a definite improvement to my bike. While off road, the steering seems to be more predictable, allowing me to get closer to the limit, making the whole experience more exhilirating, WHICH, FOR ME ANYWAY, IS WHAT ITS ALL ABOUT !
