The last "Received:" header is the closest you can get to the source.
Interestingly enough, both of those machines have reverse DNS:
[304] Thu 27.Apr.2006 19:42:01
[kadmin@archangel][~] host 70.184.150.49
49.150.184.70.in-addr.arpa domain name pointer wsip-70-184-150-49.rn.hr.cox.net.
[305] Thu 27.Apr.2006 19:56:52
[kadmin@archangel][~] host 80.168.237.120
120.237.168.80.in-addr.arpa domain name pointer dsl-2-solo-237-120.claranet.co.uk.
So, you might contact those companies, but it is possible to forge this; at least, I can bet that there's a chance they are just infected Windows machines ("zombies"). But, maybe not. OTOH, no self-respecting spammer would use their own connection....