With all due respect, I think that Beowulf cannot be contracted and here is why. In the NLS Lesson Book, in Lesson 16 specifically (16.6 Early Forms of English), it states that contractions should not be used in texts written in "Old English" (about 1100 A.D. or earlier). Beowulf is an Old English text that not only does not sound anything like Modern English, but it does not sound much like Middle English either; therefore, I think that is why it is not supposed to be contracted. If it were in Middle English, it would be optional, and if it were in an even later form of English then it would be contracted, but it isn't. Hopefully that made sense!