It is possible you could fit.
If you could drop ten lbs before your trip it might help to fit in the rides.
About 340 is the highest I have read from other posters that were able to do most of the rides.
A regular poster johde wrote this in one of his posts about size and fitting on rides:
I've uploaded these pictures before. On my last trip January 2015, I fit on everything. I'm 6'4" and was about 310. And as you can see from the first picture I'm proportionally big everywhere. On Forbidden Journey, it was a real struggle and a couple of time I didn't get situated in time and had to take the walk of same and try again. I eventually had a nice TM who spent some time and we figured out how to get it to lock quickly. The FJ pick show the maximum safe riding position. ROTM and Gringotts I sat in the back row most of the time. But I did fit in row 3 one evening when the ride was a walk on and they had me sit there.
Do a search on his name in the upper right hand corner of the page and you will see pictures of him and his posts of where he fit and where he had issues.
Some people have issues for rides and others don't for different reasons.
I tried twice in October to ride Gringotts and did not fit in row 6, which is the modified row and row 1
It wasn't height or weight issues but leg
I could not bend the leg in order to have the bar across the row to be down.
Tried two rows and gave up but will try again on my next trip
I was five months and one week out from TKR and had no flexibility to bend the leg for sitting in the ride.
Wish you the best that you can do the rides all you want!
Thank you, Macraven!
I would really love to do the coasters! I did them back in 2004, but when I went back in 2009 they kicked me off from Hulk, DD and all coasters in Island of Adventure. It was pretty horrible.