I think you're thinking of the British 5at, built for tour services.
Err, not just the 5AT, 60163 is sort of a new loco, but also a mix of old technologies. The team could not rebuild an A1 to the same exact specifications, as some specifications were a) vauge and B) some of the equipment no longer exists.
For example, to make the boiler, they got it done in Germany, who were used to building large steam vessles, we (the Brits) no longer have the technology, or the skills for the right price. The firebox was steel as well, the loco have to have 25mm shaved off the top of it. Etc, etc, read here for more info:
http://www.a1steam.com/
As for the debate, if you got locos of simliar ages together with simliar power classification, then neither Diesel or Steam will win. Diesels do have a lot of advances in control to stop the wheels from spinning for example and the wheels are smaller, to stop or reduce wheelslip (greater surface area and weight causes wheelspin?), you also got other considerations, Diesel would have field divert coils, which are active at a certain speed, to increase the speed of the motor, plus at slower speeds, you got starting resistances, to asorb the current the motor is taking. Then there is the speed up/slow down cycle of the diesel engine and one can't just throttle it to the summit on either traction, you would just slip allover the place. Additives in the fuel can inpact on performance as well and even some slight mechanical faults. Is the engine burning oil? As soon as a cylinder looses compression, through worn rings, or other ways, you loose some power. Although I am simplyfying matters to Diesel Electrics, we have Diesel Hydraulics to worry about (leaks loose power in the torque converter you know!
) and diesel mechanical (Wrong gear changes loose power too - An engine has a range where the most power is produced, the faster the engine runs outside of that band, the little gain you get.)
Steam does have more manual control, but you need to be effective teamwork members, good coal and a good fireman. A fireman who is going to plonk coal on coal will ensure power would actually be reduced quite significantly. Not only that, but they risk killing the fire. (The best way to fire a steam engine, is to have enough to cover the grate and burn for a reasonable amount of time, without burning to excessively or burning inefficently. You also should keep the fire even, like running a spirit level over the top to make it level.) The coal has to be of a type that is suitable on the loco. A GWR loco loves dusty coal (plonk it in the firebox, it burns and turns to dust, leaving little energy), while LNER locos like the hard stuff.
While on the subject of coal, it also must be of a type that gives out the maximun amount of energy, compared to amount of waste it produces. (Don't ask the calculations). A good driver would also be extremely useful, as they know how far the regulator should be open and what cut off setting to use.
Electrics would probably win, as long as someone hasn't fiddled with the wiring (That makes a lot of difference, wiring induces resistance, thus heat), the motor brushes and contactors are in good order (any contactor that doesn't contact properly, is inducing heat through resistance, lowering the power rating). Ac locos would probably need more involvement, as early AC locos used tap changers, rather than fixed notches controlled by pneumatic cams which I believe there are a lot of and each one contacts a contactor.
A good thing about electrics, is the power that goes in, is 90% or more efficent, meaning the more power that goes in, 90% of it is movement, the same argument could be leveled at Diesel Electrics, but generators only are 45% or so efficent. (45% of the movement energy goes into electrical energy)
Steam is something like 10-15% efficent, I can't remember how efficent.
To technical?