"cartel case and MBW case won't take a gen 1520 movement out-of-the-box: for starters, the cartel case and mbw case have different crown/stem/tube height to a gen case."
MBK cases will accept a genuine rlx 1575 date movement but the dial window is machined for a 26.0mm 55xx dial so it is in reality a 1680 case with a dial window machined for a 55xx dial. It is not difficult to open the dial window up to 26.5mm if needed. The crown position is basically the same as on a genuine 1680, not a 55xx, that is why it looks wrong. To use a 1520, 1530, 1560, 1570 you will have to use some 1575 date parts to position the movement correctly in the case.
Some cartel cases will accept a rlx 15xx movement, many will not. For example, most 55xx and 1680 cases from 'Paul' (Abay) will accept a rlx 15xx date movement and the dial window is 26.5mm same as rlx 1680.
Rule of thumb - a case made for an ETA 2824 will usually accept a rlx 1520, 1570 etc no date mvt...a case made for an ETA 2836 will usually accept a rlx 15xx date movement providing the inside diameter of the case is big enough and the dial window is the right size.
For more details, see "Building an MBW sub" in the sticky above the rlx section.
Jovi75...
Good luck! I know it is not easy putting one of these projects together but the more you can learn, the easier it will get.
Experience IS the best teacher...but it is also the most expensive.