I used to think this also. Then read this at Moparchat. Any validity to this?
"Magnum Heads (5.2 vs. 5.9)
There ARE actually two different castings for production Magnum heads, Apparently the 5.9 heads made in Mexico (machined at Toluca) and the 5.2 head made in the USA (machined at Mound RD). I donÂ’t know when these changes were made or if they have been there since the Magnum engines were introduced.
The major differences are listed below:
1) The intake port volume is 10cc larger on the 5.9 head (about 162-163cc).
2) The intake port is about .100 taller on the 5.9 head.
3) The valve guide boss in the intake looks smaller on the 5.9 head.
4) There are several minor differences in the physical appearance of the castings, most obvious is a little “hump” between the exhaust ports on the 5.2 head, this “hump” is not seen on the 5.9 casting.
SPECIFICATIONS
5.9 CASTING
Casting # 53006671
Machined Part Number 53021139
Intake Port Volume 162-3cc
Castings made at Cifunsa in Mexico/Machined at Toluca
Included on all production 5.9 engines built at Toluca
Mopar never sold this cylinder head separately as a service part
Mopar Performance Magnum crate motors are equipped with this casting on all Arrow Racing built/reworked engines
Mopar Performance crate motors now built/reworked by Cummins include these heads (since the Mound Road heads are no longer available) Earlier motors built/reworked by Cummins up to mid 2001 included Mound Road heads.
Mopar Performance Cylinder Heads P4876257 and P5007086 are now made from this casting (but there may be mixed stock in the depots since the 5.2 head was used up until the Mound Road Plant built-out).
5.2 CASTING
Casting # 53020466
Machined Part Number 53021137
Intake Port Volume 152-3cc
Castings made at New Haven, MI/Machined at Mound Road Engine Plant
Included on all production 5.2 engines built at Mound Road Engine Plant
Mopar sold this casting at dealers to service both 5.2 and 5.9 engines from ’92 to ‘01
Mopar now sells this a Re-Man cylinder head since these heads are no longer available from Mound Road.
Mopar Performance Crate Motors included these heads when Cummins started building them (up to mid 2001).
This head is no longer available from Mopar and has been “ruled” to a Re-Man head R5852426 (since mid 2001)
Mopar Performance Cylinder Head P4876256, when it was available was the same as this cylinder head."