Thanks to JRad (Jared) for contributing the "SpaceX Falcon Heavy & Falcon 9 Block 5" (thing:4101254).
I made it and it turned out great.
I need to touch up my paint and then I'll post a "Make".

I did have lots of trouble printing the Landing_Leg.stl files.
I mean lots.
Most of my issues were my own bed adhesion limits (fixed now) and some slicer settings that can help.

I wanted to remix the Landing_Leg with some in-model support to help get my success rate up above single digits.

Jared kindly uploaded the STEP files for his Falcon thing on request.

I hope this will help anyone having trouble like I was having.

Thanks again to Jared for the thing and STEP source files!

MAKE SURE YOU READ THE NOTES!!

Creality

Ender 3

Doesn't Matter

No

.2

20%

The STEP file imported into FreeCAD and the direct print of the Landing_Leg wound up being a little smaller than the from the original thing.

I wanted to scale it in FreeCAD before publishing but I found the scaling value would not accept the number of significant digits to make the part come out exactly the same as the original.

You must scale this in your slicer to make it print at the same size as the original!

* Use a scale of 107.62% to make it exactly right **

I use Cura and it allows that precision in the scale factor.
I hope your slicer does too but I can't help you if it does not.

I had to use "brim" bed adhesion to ensure good stability while printing.
You may or may not have to do that.
I suggest just using a brim.