This is going to be long, so I apologize in advance.
How much do you want to spend cuz here is the minimum -
Cost of heads - 400+ you can get them from navigators, marVIII's, aviators, marauders, or cobras. They're not exactly hard to find, but you definitely want tumble port or 03/04 cobra. 2004+ heads have a fully threaded spark plug well (important for boost), but they run about 1200 minimum. You can probably find the cam covers in a scrap yard.
Cost of Cams - 0-1100, if you're lucky, you may get a set of heads that still have the stock sticks. If not...cha-ching!
Cost of an Intake manifold - 400-800 either a mach 1, or a cobra unit is required, hopefully you get the TB + the intake piping in the deal.
Exhaust - 0-400 hopefully you get a set of manifolds still attached to the heads, otherwise once again...cha-ching!
Cost of Timing cover - less than 50 bucks from a salvage yard probably.
Timing components - $580 is the cheapest kit i've seen (MMR). Do not recycle used components, get new ones.
new engine valley cooling crossover pipe - $90 from a dealer.
Misc parts - $500, while it probably won't cost that much, you better have a slush fund just in case, the head changing kit alone will be $140. You will need misc hoses, gaskets and other such items.
Dyno + tune - 350-700 depending if you already have a flasher or chip.
You can run this setup off of your pcm, do not use a cobra pcm if you can avoid it. You will have to get it tuned though.
All of that to get you a whopping 250 at the wheels, because you will go down to about 8.8:1 on your compression ratio with stock pistons, and you are still turning a cast crank (its not really an issue though). These heads absolutely need high compression in NA form. So add another $1200 for pistons, rings, block honing, and rotating assembly balancing. That will get you back to a stock power level of 320 at the flywheel.
For a conservative estimate of around $3900 not installed thats what you get. For that, you could spend an extra 300 and buy a brand new crate motor out of ford racing for 4200 or spend 1500-3000 for a used motor including computer and wiring harness.
If want to use that M112 blower instead, plan on an extra $900 over an intake manifold for a used stock 03/04 cobra blower. That will put you at about 360-380 rwhp. No sense in paying extra for the Tork Tech unit since you are using 4V heads. I'll just assume you are staying NA for the rest of my rant.
Assuming you still want to do the swap, you could try to install all of this yourself, in which case you are just out your time, blood, sweat and tears. Or you could pay somebody $2000+ to do it which would bring you to a grand total of just shy of 6k.
All this is assuming pricing for stock level equipment which will get you to maybe 270rwhp, if all those used components are still in good shape. If you want to get to just 350rwhp on a 4v, which is about the maximum a 2v can do NA, you will have to at least come up with cams, exhaust, and intake tract.
Thats another 1100+800+300=2200 bucks. Which brings you to a total of around 8 grand.
How much power to you think your 2v will make if you throw 8K at it? HMMM.....
The bottom line is that the only real advantage of the 4v compared to the 2v is the increased flow through the head. That's it. A good set of ported 2v heads can eliminate that shortcoming easily. A set of Trick Flows will more than level the playing field versus stock 4v heads.
Remember, you are only working with 281 cubic inches. Your engine can only process so much air per cycle at atmospheric pressure. So what if the next guy has ported 4v heads that flow 300cfm. He has to rev to 8000 RPM to make real use of it, and he'll be losing out on torque to you accross at least HALF of the RPM band .
I'm not saying don't do this, and I'm not trying to beat you up on it. But the reality is that you can keep your heads and make (up to a point) all the power you want despite having half as many valves. Call Ron at Fox Lake, they are one of the best 4.6 shops in the country. He'll be the first to tell you that a set of properly prepped 2v heads can support 1100-1200 hp.
If you need/want more power than that, I guess 4v is the way to go.
Hopefully I have helped you out, I am not trying to snuff out your desire for a 4v because they are indeed impressive. I just want you to get the most from your money, and I don't see a four valve conversion being the best option. I would recommend either a built 2v or a crate/replacement 4v
