The Old Spanish pronunciation of ‘v’ is exactly like the prononciation of the /b/ in Modern Spanish. This sound change from Latin stayed consistent through old to modern Spanish. However, there is a difference between /b/ (word initial, or after nasal consonant).
In Old Spanish the letter ‘ç’ and ‘c+i, e’ are pronounced /ts/ but later evolved to ‘c’ which is the phonemes of the seseantes varieties.
The Old Spanish pronunciation of ‘x’ is /sh/. But over time, due to a consonant shift where sibilant consonants became non-sibilant fricative sounds.