Nicely, nicely, Sporty Spicely!
I like it when practice agrees with theory; it means the theory must have been right!
In the UK, 4kΩ was REN=1 and a line is guaranteed to support up to REN=4, so your 3650Ω was not far off at all. The voltage ratio of your transformer was about 6:1, so we'd be looking at a 20-0-20 mains transformer. That's an unusual value; 18-0-18 or 24-0-24 would be the nearest likely available (lower voltage ⇒ lower power ⇒ lower REN).