Jeff - here's a lesson from Thiel history. All our products shared the same goals of flat frequency, phase, time, and dynamic response. The family signature is quite similar between models. Also, along the time-line, new technologies were invented and incorporated, so a newer product will always be more sophisticated than prior ones. Higher model numbers get you more bass. In your particular case, you will sacrifice bass extension and power going from your equalized, sealed 10" woofer to the 2.4's reflex 8" woofer. (Unless you weren't equalizing your 03.) The 2.4 is a highly mature product, whereas the 03 is the first generation of its format. Huge difference in subtlety and sophistication, but very similar family resemblance.
Notes about your 03. Only 500 pair were made before the upgraded 03a (2500 pair.) Your 03 is the base on which Thiel succeeded. Its phase/time coherence was unique and the equalized bass was unusual and powerful. They earned immediate distribution and reviews in Europe which seeded interest from east coast US dealers - and the rest followed. The 03 is quite rudimentary compared with later models, but in 1978 it shone quite brightly.