"Saruman, his name among Northern Men, contains the Anglo-Saxon word searu, saru 'skill, cunning, cunning device.'" (UT)
"4. Back Mutation [in Old English:]
Appears before liquids and labial consonants (i.e. r, l; p, b, f, m):
i > io (hira > heora)
e > eo (herot > heorot)
a > ea (saru > searu)"
[therefore we have to use the latter form in a modern text using OE unless stated otherwise]
"ea begins with the sound of e and glides towards the back of the mouth, giving a sound not unlike that in 'bared, Baird'; "
As for the -man, it is really a matter hardly to be grasped in modern ENglish at all: "root-stems which according to Germanic laws of Ablaut, change the root vowel during the declension. In Modern English such words still exist, and we all know them: goose - geese, tooth - teeth, foot - feet, mouse - mice etc. " The form is 'mann' in some, 'menn' in other places. Since Tolkien anglicized as far as possible (see app. F), we can probably say [mæn] throughout.
I suggest the sites
Pronunciation of Old English and
The Historical Grammar of the Old English Language , from both of which I have quoted.