If you build it +50 I think you will have quite a few problems.
1) any fibreglass body parts will need to be altered.
2) Suspension wishbones will need to be altered.
3) drive shafts will be short.
4) the mx5 front steering is a problem with the track rod ends touching the wheels.
Just to name a few.
Phil from Talon made lower wishbones with a bend in them to get over it.
I think it might be better to look at making the tunnel section smaller.