"Q1) If one has a published ground track and speed of a given a/c along said track but lacks the altitude can a discrepancy between the speed and distance travelled be interpreted as a change in last known altitude?"
Quite possibly. Let's say the a/c is flying at an Indicated Air Speed of 280 kts and is flying in an International Standard Atmosphere condition at 35000 ft. A tail wind exists of 30 kts.
It will have a True Airspeed of 488 kts, giving a groundspeed of 518 kts.
However, it then descends in the next 7 minutes at 3000 ft/min to 15000 ft where there is a tailwind of 15 kts. At the same Indicated Airspeed it will now have a True Air Speed of 347 kts and a groundspeed of 357 kts.
All the ground observer without a height readout will have seen is a 31% reduction in groundspeed.
"Q2) A commercial heavy enters a 60deg turn at 430 knots, exits the turn one minute later at 350 knots and within two minutes has accelerated to 500 knots can any reasonable assumption be made regarding altitude fluctuations of the a/c in question?"
At 28000 ft and 280 kts Indicated Air Speed, the 'heavy' would have a True Air Speed of 432 knots. If it reduced speed in the turn to 240 kts Indicated Air Speed and descended to 25000 ft (quite feasible) it would then have a True Air Speed of 349 knots. To achieve 500 kts True Air Speed in the next 2 minutes, assuming it has a maximum permitted speed of 310 kts Indicated Air Speed or Mach 0.86 (whichever the lower), it would have to climb to 33000 ft and accelerate to 310 kts Indicated Air Speed. A climb rate of at least 4000 ft/min which isn't very likely, unless it was very light indeed!