Well, if you have a JDM header, and it has a 2.5 inch collector, that's what you will need, but correct me if I'm wrong, you said you already had the header, and if this is the case, the header wouldn't have bolted up to the factory cat, you would have needed to have a new flange welded on. If you didn't do this, you don't have a real JDM header, which is bad, in the sense that it doesn't flow as well, but good in the sense that you can run a USDM 2.25 inch pipe size, which is much easier to find, and ussualy less expensive.

As far as $1800 for cams, springs, and retainers, you should immediately go to his shop, and back hand him across the face for thinking that you were such an ignorant moron as to pay so much money for cams, springs, and retainers, and explain to him, that you would rather not pay over retail for things.

Call around for these cams, try randdmotorsports.com and ipsracing.com they both sell them. As far as springs and retainers go, use skunk2, you'll save your self hundreds, and there is almost no difference in quality or workmanship, and definitly nothing in functionality.

And what he reffered to, is "porting" and "polishing", two seperate terms, porting is actually enlarging or matching the ports of the head, or changing the flow characteristics of the head, by changing the way that the head is contoured in the valve ports and combustion chanmbers. As far as polishing goes, it's exactly what it sounds like, ussualy done in a swirl fashion, basically just to smooth out the air flow. This can be a very expensive task, and should only be done by very few place in the country. And if you do plan to do this, you should have the same person install your valves, as they will more than likely do a three angle valve job as well, and by installing the valves, they will also do the springs and retainers. The few shops that I would say are capable and good and doing p&p's are as follows:

Endyn
JG edelbrock
Port Flo
Jun (who as I understand is no longer around in the US)
Signal Auto
King Motorsports

Now of course, I"m sure there are others, and keep in mind this is only my opinion, but those are the fgew world class Honda auto shops in the country, that actually us flow benches, and proven methods. On a side note, you should be prepared to spend close to, or in excess of a thousand dollars, just for the labor of the port and polish, which is pretty much all it is, is labor.

Later,
Aj