Mystery Poncho Parts

[Guest]

Any Pontiac guru's out there?<P>A friend of mine recently picked up a set of Poncho heads and cannot identify them... I said I would help and he gave me the following info:<P>598177 (# above centre two exhaust ports)<BR>F61 (between centre valve springs)<BR>8 (outer near one end)<P>If possible, what was this from, and what does it fit? Has screw-in studs and fairly small looking chambers...<P>Any ideas?<BR>