That's still a pretty tall tire for the front. It could cause issues with the tire rubbing on the frame at full lock. Plus it will effect how much you can lower the car, I had to remove my fender braces even with my 275/40/17's.
The 9" rim isn't a problem at all. I've been running mine for years now with a 17x9 in the front with no issues.
Switching from drums to disks will widen the track in the front by about a 1/4" if I remember right. With a 17x9" and 5" of backspace and a 255 it probably won't make much of a difference. With a 275 you'll be very close to the frame at full lock with the drums, and very close to the fender with full compression (turning into driveways etc) with the disks. The other way to do it would just be to run a small spacer with the drums, then remove it when you switch to the disks. Might not be needed if you don't get any frame rub with the drums.
Thanks for all your explanations, there are a lot of questions but this does really help!
Its so hard to know what variables are critical. I was assuming a 9" rim might be part of a fittment problem but maybe not... Comparing 255/45/17 to 275/40/17, the 255 is actually taller by about 0.4", but the 275 is wider by about 0.8"
http://www.tacomaworld.com/forum/tirecalc.php?tires=275-40r17-255-45r17 Is removal of fender braces necessary with the 255's?
As for the width of the brakes, is that generally true of any conversion kit?
I put 17" AR Torque Thrust II's on my '71 with Nitto 255-50's on the front and 275-50's on the back with a stock rear end, XHD leaf springs.
Nice looking setup! Have you been able to road test the fitments? Any mods to the front end?