what springs are you using?
I have toyota springs on my sas and the toy springs are slightly narrower- like 2-3/8" as compared to the ford's 2-1/2" spring width - I'm talking actual width of the leafs.
For me, it's no big deal - I just used a couple washers for spacers, but if those hangers are made to fit toy springs perfectly, other, wider springs may not fit - just a thought.
But I know some toy guys are using the waggy leafs for their sas's, and those are 2-1/2" like the ford's, so it'd probably work fine.
Don't know about marlin, but some companies offer a different crossmember when using a toy axle or a dana 44 - I assume their matching the waggy spring spacing on the d44 style, but not sure.
But if you have to cut and modify a crossmember, you might as well just save the cash and just buy the leaf hangers and some square tube and make your own.