While this is a bulky looking suit it is not a horrible basic design. But add the double width and maybe really long cannons under the arms and it starts to look just bad.
Dave Taylor then models up one with the Grav Cannon on the shoulder and a siege drill replacing the whole forearm and fist off one arm. It is a significant improvement but has the problem of not being a legal WYSIWYG model for someone who actually would field the unit. It translate fine for Grav Cannon mounting since that is really just a single cylinder as you can model the amplifier part else where which shoulder mounted give you a look like a Battletech Thunderbolt or the Forge World forces of mars walker sculpt. I actually thought of using the forge world models directly as grav cannon centurion count-as before seeing Dave's conversion but they are like 50 dollars each so no room to complain about the Centurion kit cost if you do that.
But if you want the TL lasconnan or heavy bolters this is a bigger issue. I do not think you can bundle them together and put them up there. True to envision a razorback turret sitting on the shoulder. Not going to work. If it was a single lasercannon you could model it holding it like a gun for a very robotech look but two will look bad like that and the double barrel seems to big.
You probably need to look at the forgeworld heresy dreadnoughts for a idea of how to replace the whole forearm and fist with a twin linked heavy weapon as again you really cannot just add a razorback turret on the arm. It will need to be compacted somehow
Freshcoast 40K has a post where they show the Centurions without the crotch guards which make the models better but the upper legs then need some embellishment added since they look to plain.