no need to cut the tunnel ,if you can get away with using a standard tunnel then life will be heaps easyer when (or if) you need to engineer it

its been done heaps of time without chopping the tunnel

ive found it help if you bolt the crossmember to the motor first then slide it in from the bottom ,that way you can just lift it up and not struggle to clear the steering arm thingo

might be an option ?

good to see this thing is coming along very nicely !