I won't be racing the bike...yet. I'm saying it can change the steering characteristics due to being wider, and the rear may run out of grip way earlier than the front tire. I'd replace the front wheel as well, it has gouges on it and a somewhat noticeable bend.

Another thing here is rubber sourcing. 150s are relatively easy to source (Michelin seems to have Road 5s) but a rim-perfect 140 isn't. Maybe I'm just too nitpicky about this but at least it isn't too much of a pinch

You're unlikely to notice it or run out of grip on a road

I won't keep the stock wheel if I get it with the front end parts swap. I'm just worried about the front wider than what it supposed to be, while the rear stays the same

I'll just try and source another set of forks, maybe from the other 400s, the earlier GSX-R750/1100 or even the FZR/YZF 750/1000 front end(needs a respring and probably valving) and try if I can call out for a Thundercat front end.

Make sure the front wheel has a speedo drive - the 3en1 has a Japanese speed restriction that needs the original speedo

The limiter wiring is already cut off, don't even see the wiring for it anywhere. But since the innards of the original(broken) speedo is intact, I can use it if it really needs it, when it won't do atleast 190 km/h

The cdi has to get s signal at zero or it limits to 12,500rpm in every gear

Sorry for being away for a long time...needed to take care of financial issues...

No prob with the 12,500 rpm limit. It had gone 13,000 with no issues

I have had three different front end conversions between two 1WG bikes. First was YZF T-Cat front end swap including the front wheel. Straight bolt on affair. Forks and brakes were a significant upgrade, but I steering feel was not as confidence inspiring. The bike "felt" like it wanted to drop into the turns much faster, but at least it held a neutral line once initiated. The T-Cat fork off-set is about 5mm less in the triple clamps than FZR, but the tire is smaller diameter at 120/60, so trail should have been the same. Who knows. I think it was probably just the profile of the used tire that came with the package.

Next was 1st Gen R6 already fit to a bike as a bought it. The steering stem needs swapping, but retains the FZRs geometry. Forks are soft, and I didn't really feel it was worth the effort. What I have settled on is '08 R6 forks in '05 R6 triple clamps. I swapped the FZR steering stem into the R6 yoke, and ran R6 front wheel. This set up gave me the fork length I wanted and the triple clamps retained the FZR's geometry. I run a 120/70 r 17 front tire. Forks are a major improvement, brakes have all the one finger stopping power you could want, and steering is very much like original. Light, neutral, and takes easy corrections mid turn with out drama.

If I were in your shoes I would probably be looking for something straight forward that maintains the original geometry. T-Cat kind of fits that bill if you run a 120/60 tire and worthy of consideration, but I would be tempted to source FZR600 forks and rotors. Then put some straight rate springs in the forks with cartridge emulators. You retain original geometry/wheel size, and get a performance upgrade in the dampers.