I agree the chamber is as cast.

As for the quench comments.....carefully note I said you won't see any gains on this engine. I wasn't talking about all engines, especially 'hi-performance' varieties.

I also will note the reason most all aftermarket heads are closed chamber is the need to achieve high compression ratios....a smaller chamber is usually key to that. A small chamber is usually a better way to achieve CR than a big piston dome.

If a piston fills the 'open' chamber to the same quench as a closed chamber, the engine won't know the difference. But normally, it's simply easier to make a closed chamber and then use a flat top piston. That's why it's done that way. My comment was to point out that while 'cool', the closed chamber Slant head isn't going to allow someone to reach a place otherwise unattainable.

Rob, are the valves stock size diameter or os?
And is there any visible or easily measured difference in the ports?
When you cc the chamber maybe also cc an intake and exhaust port.

I'll surely do it. No, the valve sizes are stock. I'll post up the port volumes with the chamber volumes tomorrow, when it's warmed up a little. lol

Oh and I asked the seller if he knew what the head originally came off of and he did. It came off a 1977 Dodge Aspen. So.....I guess no Apsen is safe in the junkyard now. LOL

find it odd that what is clearly a non-standard head was assigned a standard production part number.

I stand corrected. Congratulations. You bought a "unicorn." I am interested to find out what the combustion chamber volumes are. I find it odd that what is clearly a non-standard head was assigned a standard production part number. But maybe Chrysler just used the same mould for the body of the head and changed mould for the combustion chambers.

from back in my Foundry days,,, if at all possible Engineering would use as much production content as available when having special - trial parts cast. That was done to minimize costs and to also not introduce other variables into the evaluation process that the special part would be subject to. Typically the molding tooling, what makes the exterior of the casting was made with 'inserts'. The inserts would be changed out periodically as they wore, so Engineering would only need to pay for a special insert and use the remaining production tooling to produce the rest of the casting that did not change.
Concerning the part number, the part number on the slant head is on the top side of the head, that would be what was called the cope mold. The combustion chambers are in the bottom of the head or what was called the drag mold. What IH / Navistar did was change the cope part number for Engineering castings to a X part number, Chrysler surely did something similar. The cope and drag molds are made on separate machines then joined together. Possibly what happened is the part number on the cope was not properly coordinated with the insert change on the drag so there would be a special Engineering casting made without the special part number. That happened occasionally, remember back in the 70's computer and machine logic controls were in their infancy. The call when to change the cope mold part number then to change the drag insert so they match up at the proper time, and then of course to change them back to the regular production configurations would be made by the line Foreman, and he was probably juggling three other issues at that same point in time.
Whether this is what happened is only speculation, but it is within the realm of possibility.
With the production part number on the head, it is also possible that the head under discussion went through the remaining foundry processes, was machined then assembled to a production engine was installed in a vehicle and sold. It has happened before.