And now for the last few lines...
 
Hann setr við holan lófann ok tekr svá við knútunni, þar fylgir leggrinn með...
You got the meaning of this - one or two minor points...
The object in all clauses is in the singular "lófann", "knútunni", "leggrinn".
Also "við" can either be a preposition or an adverb depending on the context.  Here it is an adverb.  According to Gordon´s glossary as an adverb, "við" can be translated as either
at this, thereupon, back, against, at it.  "setr" can either be 'he set, placed or put' so literally this can be translated as 'he set, placed or put the hollow of his palm at it" i.e. he cupped his hand.  Jed, according to my lecture notes and the translations by Byock and Jones, "setr við" is nothing more complicated than this.
"Þar fylgir leggrinn með" implies the leg-bone was attached to the knuckle-bone.
 
Böðvarr sendi aptr knútuna ok setr á þann sem kastaði, ok rétt framan í hann með svá harðri svipan at hann fekk bana.
Interesting that you both have 'in his face' for "rétt framan".  I know in modern Icelandic "í framan" can refer to the face e.g. hann var fölur í framan - he was pale/his face was pale, but here it is an adverb meaning directly at (him).  This concurs with Byock's and Jones' translations - smack at him, into the man.
 
Hope this is helpful.  I'll post up the next section in a day or so.  If anyone else wants to join in, please feel free.
 
Kveðja,
Sarah.
 
p.s.  do you want feedback in such detail or is the grammatical side rather off-putting?  Let me know if I'm boring you!!