What would be the expected result of a re-engineer or rebuild?
Depends how far they would want to go with any such scheme...
But the theory AIUI with such schemes, would be to re-engineer or rebuild the locos with more modern equipment ie. A more powerful and economic engine, potentially AC Traction motors over the more normal DC, replacing older rarer parts with newer more modern and easily available items, as well as extending the operating life of the locos beyond the originally planned operating life.
Recent examples of such schemes would be the ongoing schemes by RVEL/NR and the separate BRUSH/GBRf projects to modernise class 73 locos with either a pair of 750hp Engines (RVEL) or a single 1500hp MTU lump meaning you should end up with locos that have more modern engines, a winder operational range, and still have the option of powering them using the 3rd rail.
Then you have the BRUSH/Eurotunnel scheme to modernise/rebuild original (or just older) Class 9 locos (not the shunted class if your confused) to the more recent and more powerful Class9/7 spec as class 9/8s
Another obvious well known example was the scheme to modernise/rebuild class 47s as class 57s with a more modern (than the Sulzer Power unit) and reliable GM/EMD 645 engine (albeit a refurbished engine, not a new one) as well and improve (to a point) the cab conditions ... mainly a repaint and stopping some draughts IIRC
And the well known to most enthusiasts, of the modernisation of HST power cars for use with NR, GC, EC, and FGW with new Engines, overhauled electrical equipment, new cab desks and gauges etc, new/replacement wiring etc to the point that they had (once again) a more modern, reliable and economic engine that was/is fit for use for something like another 15/20 years (at the time of rebuild/modernisation)...
You also have schemes where BR had looked at modernising some locos ie. With newer replacement engines... but these didn't really go ahead, other than small scale fitment of newer/different engines to a few class 37 for a proposed new type 3 loco.
For such a scheme with the class 60s you could potentially end up with (at the extreme of the scale) New more powerful, yet economical engine... AC Traction motors to increase haulage capacity... Improved cab conditions with New cab desk and dials, air conditioning, all safety equipment (ie AWS, TPWS, OTMR, and future proofed for ETCS) being fitted into the panels rather than "tacked on" as equipment is required to be fitted... new compliant light clusters... standardised Fuel tanks to provide the same fuel capacity on all the locos WABTEC leases or resells... depending on the potential operator and the engine fitted you could end up with the likes of the AAR multi system being fitted to allow use in multi with class 59, 66, 67, 70s etc
There is too much to realistically speculate on since you don't know if they will just be overhauled like the DB "Super 60" project and returned to traffic, or if they will be modernised/rebuilt to a WABTEC spec or if it would be to the potential operators desired spec, technical and physical limitations and budget, as well as what other hoops would have to be jumped through to satisfy the EU dictators
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