Ok, I sharpened my pencil too. Your assembly is nearly n exactly like mine with the exceptiom that my combo runs aluminum heads.
I used the Wallace Calculator.
I used these inputs 4.03bore x 3.58 stroke, with the standard 6.123 rods and an ICA of 59 degrees for the 262 cam. The calculator spits out a Dcr of 8.88 and cylinder pressure of 183psi. To get the 183, I had to input a Scr of 10.7, exactly where mine is currently. To get a 10.7 Scr from the above specs requires a total chamber size of 77.14cc
Still working backwards, this requires some combination of parts and clearances to achieve and is all too easy. Mine was set up with a 4.04 bore, .003 pop up(-.6cc), 5cc eyebrows, 63cc heads and the standard .039 fellPro which I think is 8.9cc.
Doing the math, this totals 76.3cc. My swept is 752.03cc. So (752.03 + 76.3)/76.3 =10.856 Scr.
Now if your overbore is .030, the your swept is 748.3cc
So (748.3+ 77.14)/77.14=10.0700Scr.
And to make the 77.14, with an 8.9 gasket and 5cc eyebrows, requires some combination of head and deck height to total, 77.14-(5+8.9) =63.24. If the KB107s are slightly down say .003, that would be .6cc. so that leaves 62.64cc in your heads.
The point of this exercise is that 182psi is easily possible with the parts that you have and that your Dcr is too high for iron heads and pump gas. I run my combo on 87 and full timing so I know it's not too high for aluminum. There are several guys on here that run quite a bit more Dcr on pumpgas.
But that doesn't help you cuz aluminum heads are not cheap, and for your intended useage really aren't justifiable.
So the way I see it, the money has already been spent on the heads so let's try and keep them. That means you are gonna have to manipulate the Dcr with the other parameters, namely ICA,gasket, and pistons. Since you reall want to keep that little 262, that leaves gasket and pistons. Since the .039 FellPro is a tuff sob and it sets a nice tight squish on closed chamber heads, which yours kindof have to be to be down at around 63cc; That just leaves the pistons.
So your pistons either have to be modified or swapped out.
To mod your pistons will require a reverse D-dome, to maintain the squish. I don't know if the 107s have enough material in the crowns to achieve that, or even if it is permissible to cut them,or if it is cost effective to do that.. But I do know that KB makes pistons with pre-cast cups like that.They are the KB232s with 18cc cups. They also have a nice .050 quench pad that you can use, actually;have to use, to adjust your squish. So lets do the math with those installed; Your heads are around 62.64, the gasket 8.9, no eyebrows , and 18 cc in the cups plus about .64cc in the deck. That totals ; 62.64 + 8.9 +18 + .64 =90.18
And.....(748.3 + 90.18)/90.18 =9.298Scr plugging that into the Wallace calculator gets us a Dcr of 7.75/153psi. That is really good for your intended useage. But, firstly the Q-pad will need to be machined down to fit and if you ever want to upsize the cam, you have no place to go; so this engine is kindof written in stone,that is to say no cam-change allowed. But it will burn 87, and it will be a bit of a tractor as to torque.
Now on the off chance that the pistons were down a little more than "just a little", there is room to pre-plan for a future possible cam-swap. There is some room in the Dcr. So since the pistons are coming out, this would be a good time to maximize the Dcr, by a little decking.The above described combo at a Dcr of 7.75, could be bumped up to 8.00 and still run on pumpgas, probably still on 87. That means by re-decking to make the 8.0, you have room for a larger cam of 1 or maybe 2 sizes.
Keep it mind I made up all the number here for your perusal, the big picture being you are not sunk yet. Get the numbers; head CCs, Deck HT, and we can help you dial it in, and so should your builder be able to.
Now if you wanted to put a different cam in , um...new solution.......lol
But I gotta say a 7.75 Dcr in a 360, in your chassis and for your useage, will not be disappointing.153psi is a pretty decent number.
