these two articles are part of a series of boron hydride papers in vol. 75 of JACS. the usual, but with some nice details not found elsewhere on this site, except perhaps in the
Post 253798 (missing)
(PolytheneSam: "NaBH4 patents", Chemistry Discourse) patents.
The Preparation of Sodium Borohydride by the High Temperature Reaction of Sodium Hydride with Borate EstersH.I. Schlesinger, Herbert C. Brown, and A.E. FinholtJ. Am. Chem. Soc. 75, 205-209 (1953)(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_imgs/djvu.gif)
Procedures for the Preparation of Methyl BorateH.I. Schlesinger, Herbert C. Brown, Darwin L. Mayfield, and James R. GilbreathJ. Am. Chem. Soc. 75, 213-215 (1953)(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_imgs/djvu.gif)
...and apparatus for producing same. relevant to the above if you don't have anything else to do.
Sodium Dispersions, pp. 6-10
and
Sodium Hydride, pp. 10-13
of
Inorganic Syntheses Vol. 5.
(https://www.thevespiary.org/rhodium/Rhodium/hive/hiveboard/picproxie_imgs/djvu.gif)