Your not considering the whole "New package"

You are fitting engine, gearbox and propshaft, diff, and drive shafts (unless the Calibra was 4wd) Extra to the original.

The new car/set up will be heavier, but the balance will change from front heavy to more centred.

You may be adding 70kg forward of the Front axle centreline but you are adding weight behind the front centreline, gearbox diff etc. as well which will counterbalance some of that 70kg.

I don't know the exact layout of a Calibra but I'd be surprised if you can get the gearbox past the original Steering rack location.
The rack must be mounted very high or very low if you can.

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