If 45>60mph is yur target,
IMHO you may be going about this all wrong.
Consider what rpm you will be turning, then build your engine to make power at that rpm, not at mega-rpm where you might only be one time, and spinning so. At the top of first gear, who cares how much power you have if the tires are spinning......
With 3.91s and 28s, First gear(2.45) tops out at ~5500=43mph.
On the 1>2 shift the rpm drops to .592 x 5500=3250rpm, and so yur engine needs power at 3250 and NOT at 5500. 3250 is a tuff place to be, cuz most of the time, it's not ready for full-power timing yet, at least not with iron heads and open chambers. and Honestly, if I had that gearing problem and stuck with a 318, I would be very very careful.
Obviously 4.88s would be better, but with those, First gear is pretty useless. and hi-way cruising is out. That 1-2 split is just to big, and the only way around it is a high-stall TC.
IMO if yur gonna do something like this, I would stall it up quite a bit higher, and keep the 3.91s.
Or
go with 3.23s and get 60= about 6200 at the top of First-gear. To go 6200 your power-peak can be centered around 5700. With a torque peak around 4200, which might like a stall around 3400, for a One-gear car.
So, you get the idea.
Or
just bite the bullet and install a bigger engine which will inherently have more bottom end torque, allowing you to run less gear, and less cam.
Or do what I did, which was to install a 4-speed, which has a better 1>2 split(.72), for less Rpm drop on the 1>2 shift.
Well, actually I did both, lol. and now I can spin the the tires thru almost three gears, lol. That's not a brag, I'm just saying there comes a point where you get into traction issues; and there's no point in having all that power, just to put it into tiresmoke.
With a standard 2.66 low 4-speed, the 1>2 rpm drop is 72% which is from say 5600 to 4040, for a powerband requirement of just 1600, so now yur 318 does not need that big cam any more, for the same zero to 60 ET.
And a smaller cam will have an earlier-closing intake even, and so, a higher pressure. and now you can run a proper gear ratio combo, to hit 60 at a more advantageous rpm. and that means, you might get a hiway cruiser out of the deal.
So many ideas.
For this combo, alloy heads, just for the compression ratio, is IMO, not gonna make a big difference, because, in the first place alloy heads NEED more CCP just to break even with a good iron set. They say you need at least a half a point more with alloys, but in a Streeter, I think a FULL point would be more like it.
Then you have the 2.02 valve issue, as to shrouding, to deal with, and finally, if yur only gonna Power-peak at 5500, then you don't even need those big valves. Because, again, yur not gonna be at 5600 in Second@60mph, unless yur running 4.10s, and there goes your cruise-rpm again.
I went thru all this in 1999, and I figured it out real quick, that I would need a 5-Speed manual and a 360, to cover all the bases, to be able to use a small cam, running low-grade gas, and still be in the 12s which is fast enough for me. And still make fuel-economy that even 318 guys can't touch.
People call me a 318 hater, and this is why; Yur trying for BB results with an engine size that is just too small, IMO, for what you want it do.
I mean, if all you want to do with your 318, is one thing; like be real fast from zero to 60, OK I get it. Pressure it up, cam it up, stall it up, and gear it up, those are the right things to do.
But in the end, when you add up all those other costs, and see how focused your combo is, and how much gas it drinks just driving it around the block, and how nearly useless 4.88s are on the street, and the thought comes to you that you mightabin way happier with a bigger engine,
please don't hate me, lol.
One more time, consider your trans and rear gears, and build to the gears.
As to headgaskets
at zero-deck and closed chambers, your compressed gasket thickness becomes your Quench. This dimension must be large enough that at rpm and hot, the pistons do not bang into the head, bt not more than what will create detonation for you. Most guys target .040. Brave Dumbazzes like me push envelope down to .028, and I got away with it.
Your results may vary, but not a chance would spend more than what the FellPros can do for you.
The point is, at zerodeck, you cannot run Piston to head clearance of .020 and not expect to break something. And there is no need to go that extreme.
Like I said earlier, your swept area is just too small to go for the big pressure numbers, with the cam that you have in mind..