i just found this post, do you have any pictures of your 400?? you’ll have to come up and ride with us sometime, do you do any play mx??
i had a 440ex before, strong bike. i had a full tc shorty exhaust, xr400 cam with a wiseco 440 all bore kit, it ran right with a '04 450r full lrd exhaust. if you didn’t order the big bore kit yet, you might want to look into a 416 bore +4 stroker to get the 440cc your looking for. it’ll be better all around power over the all bore 440 kits. the xr400 cam will drop in and you can find them dirt cheap too.