From what I hear, read , and experience it looks like I am at the limit of how much can be done with a stock cam core cam.
My combo will be 550 cu inch, 572/13 385cnc heads, 14.5 or higher compression, Jesel 1.7 rockers, methanol injection, ported 3X intake, aluminum BMP Block. Since I will be waiting for pistons and heads, I should find out what benefits a new bigger cam core will provide.
My current cam core has a . 920 base circle and .510 lobe on the intake. Crankshaft is 2.2 rod bearings with 4.315 stroke.
I see . 005 or . 006 lash change around the base circle due to high spring loads when I measured lash all the way around the lobe.
Since I may need ( almost gaurantee'd) longer pushrods I am thinking a larger cam core might change that, allowing re use of what I have.
My block will grow . 011, deck height is . 025 higher, plus the 572/13 heads will be roughly . 060 thicker and the 572 valve gear may also add some length. Tally all that up and I see a need of at least . 100 longer pushrods is quite possible.
M y old combo had iron block 10.695 deck,. 920 cam base circle, 440-1 heads cut over . 060 more than the new heads will be cut. That combo needs 9.80 intake pushrods.

So back to the original question.
What advantage is there to a bigger cam core, and cost? Also is there a special part required to go with the Jesel belt drive?

From another forum asking about the limits of a 2.125" journal cam core:

Hello John348, comparing the 2.125" journal cams that we offer, to our 60mm journal gun drilled versions, there are very decent theoretical benefits with the 60mm. ("Theoretical" is a neat word, if something doesn't come out in real-life like was calculated, it's a great easy way out.). The 60mm cam will have about a 42% increase in torsional rigidity (twisting from front to rear). The beam strength (deflection between journals, such as the forces that fully open valves exert) on the 60mm is up about 70% from the 2.125". There are certainly other factors that can be considered to find absolute values, but on an apples-to-apples comparison, these are the basic figures.

When you consider the largest journal on a stock size Mopar core is 2.000", and they step down from there, it would seem worthwhile to step up to at least the common 2.125" ford babbitt bearing size.

I would call Mike Jones and check on what the current cam core situation is.

The main advantage is the lobes are larger so it is easier for the lifter wheel to follow. Helps increase valve train stability. Steve Morris has a great 3 part video on Youtube on the subject. They are under SteveTech.

There is no disadvantage to going to a larger core other than the costs to do so. Also depending what you are planning some cores can be harder to find than others. As for cost Weston Machine charges $5-600for everyone we have had done there. For anyone not close to Jersey there woudl be shipping on that as well. IMO I would not have anyone else do the work but that's just me, they are the go to for any custom block work. Charlie Weston IS the man in block machining.

Well, as you have heard, torsional loads can break the stock core size. So, that's enough advantage for me right there. Breaking a cam can be expensive. You can always back down on your intensity and loads.

The other benefit can be a higher rate of valve acceleration is possible with a larger camshaft core.