Now... I've never done it with a GL engine, but I've done it with a few others, but mostly, I did it with large valves for railroad airbrakes...
and I'm certain that if you've done it with your other engines, you'll already know this, but for others who haven't...
Find locations on the main castings that are suitable for supporting the whole unit...
Figure out approximately where the center of gravity of the fully assembled (at least, whatever you'd do in-stand) engine would be...
Cut metal tabs or tubes to support the engine, and bolt them TO the engine, orient the brackets to get to arms that would support the engine WITHOUT obstructing access to parts you'd need to work on...
Cut and tack-weld arms for those tabs... shape/bend/form them to reach to a point where you can weld them to a plate leading to a piece of appropriately-sized pipe that you can slip into the head of your engine stand (remove the universal automotive plate altogether, or adapt your GL engine plate to bolt to the factory piece).
I have several adapters to fit my engine stands... one for lower units for Mercruiser R/MR/Alpha series marine drives... one for Kohler K-singles... I even cobbled one together to hold an R-390A back when I was recovering from neck surgery...