Hiya!
I would advice using the 3.75m tanks for the SLS core stage & a 2.5m tank set for the ICPS & Orion stack. I would also use the largest 2.5m SRBs from the Making History pack, if available, so you can stretch the core stage as long as possible. I’d also use 4x KS-25s instead of the Mammoth engine part since they combined are lighter with similar thrust. To make them match SLS’ engine placement, try using 2x mirror symmetry. It’ll take some tries but eventually you’ll find the optimal spot to match SLS’ engine placement.
For the ICPS engine, if available, I would use the Skiff engine; it’s supposed to be a J-2 engine-alike but I find it’s thrust/weight/efficiency to better mirror the real world RL-10, which is conveniently the engine the ICPS uses.
For Orion’s engine, I would advise using either the Terrier engine, or the puff engine, if you feel brave enough to get it aligned through Orion’s (mk2-3 cockpit) CoM. Also, for Orion’s offset solar panels, use the earlier trick of using mirror symmetry to position the solar panels closer to Orion’s. For Orion’s tanks, use the 1.875m tanks, as that will give you a closer approximation to the size difference between the Orion capsule & the European Service Module.
Use angle snap to make sure all of your placements match, & hold shift while placing or dragging parts via the translate tool. This will allow the part to shift *just* slightly left or right, depending on where your mouse is. This will allow you to get a better, finer positioning for parts.
For the LAS Tower, I advise using a fairing for the blast protective cover, then a structural strut with 2 sets of 8x sepotrons. You can add cones where needed for aesethics. Note, to get the necessary offset thrust for it to torque the pod up *and away*- open the parts menu, pick any 1 sepotron, remove it from symmetry, & reduce its thrust from 100%, to 99.5%, that slight difference will be enough to create a higher thrust, slightly longer burning & more stable alternative to the stock LAS part which is frankly, awful in many ways as it can’t even do it’s listed job well at all, but that’s a separate subject.
Also to create the LVSA, I would just use a fairing from the core stage that meets with the upper tank of the LVSA (covering the lower tank, engine & decoupler).
Hope this helps!
PS- I will upload my replica of SLS Block 1 tomorrow which shows all of this in detail.