I'd be interested in the 1978 Giulini Ravel CD owing to the inclusion of the LH concerto and La Mer - but not the one with Schubert 4 if his (admittedly late) dire DG recording is anything to go by. At least we can compare two La Mers from him (or should that be Les Mers?).
I'll reserve judgement on Tennstedt's Bruckner until I read some reviews, though his LPO live Bruckner 3 CD was rather mediocre. He did of course make a fine Bruckner 4 (and four other LPs) with the BPO around this time (1979-1983) for EMI.
But I hope Testament are not just issuing any broadcasts by 'great-conductors-of-the-past-who-are-now-deceased' (to paraphrase Woody Allen), whatever their quality. BBC Legends went down that route and I think it backfired.
One Testament CD I can strongly recommend is the Sibelius and Elgar violin concertos by Ida Haendel and CBSO/Rattle, from 1993 and 1984 respectively. The Sibelius, from the Proms, is a very fine performance, dark and brooding, and technically first rate.