I have a mojo and have shot a lot of them of all different lengths and weights. I have shot a 45#@28 when I was shooting 28.5” draw length. It shot well with a 29" 500 spine arrow and 225 on the front. I now draw over 29". I shoot 29.75” 400 spine in my 55@29 mojo with 200 on the front with a skinny string and 225 with a standard mojo string. They like a little bit of a stiff shaft from what I have seen, but with the larger fur silencers JD uses it will slow the mojo down a little, and make it real quiet. If you shoot no silencer or real small ones for indoor target shooting it will want a stiffer spine.
For three under I would look at about 7/8” nock height for a start. It could just be me and my shorter mojo, but my bow likes a fairly high nock set 3 under.
Form makes a lot of difference as does a lot of other little things, but I would guess 7.5”-8” brace with the fur silencers and about 200 on the front of your shaft. Work point weights up and down from there to see what you get.
You will have no problem getting 400 gr. and will likely be closer to 500, and over 500 if you start working that shaft down in length and point weight up as you fine tune.
Get the test kit field points from 3 rivers. Get two packs while you are at it. I think I only got two or three of each weight, and more points of each is better for group fletched and bare shaft shooting. Also get 100 and 50 gr. brass inserts, and hot melt glue. Now you can make up a lot of combinations. 50 and 100 inserts are not only different weights, but also different lengths, which changes the effective length of the shaft. You can do a lot of combinations with that stuff, plus the original aluminum inserts. That is my personal carbon kit of parts, and I use them all at one time or another when tuning carbons.
I have found carbons to be more length then point weight sensitive. They get fairly predictable when I get down within 1” of my minimum arrow length, but when they are a couple inches longer than needed they act a lot weaker for me.
The last mojo I shot other than my bow was a 62”. All I can say is WOW! JD’s bows are very smooth. My 56” draws like most 60-62” bows I have shot all the way out to 29.5” for me, and I am sure past that. The 62” is really smooth, fast, and even quieter than his shorter bows.
JD's bows are really nice so be sure to post up some pic's when you get it.