We've had this discussion many many times going back to Airwarrior days.
Best guess since Lowell mentions a 5 blade prop on the Spit is that he flew against a Spitfire XIV.
Also best guess is that the pilot he flew against was a ranking officer named Teddy Donaldson, who had flown combat in Spitfire Is in the B of B but hadn't been in action in a long time.
Lowell at the top of his game in the 38 ate up a Spit pilot who had his combat time in Merlin Spits and tried to fly the XIV like a merlin Spit, which it was definately not.
I think it's a good example of pilot skill making the difference and getting the best out of his aircraft, which Lowell did.
As for the Seafire XV. I have the logbook of Tom Slack who was a Flight Commander with 41 Squadron flying Spit XIIs. He notes a flight on April 28th, 1944 in a Seafire XV testing a new canopy for it at High Post. So there was at least one Seafire XV floating around then.
So it's possible it's that XV, but I doubt it.
