My New Truck

[HAULIN' IT]

Personally Id get the correct LS dip stick. Option Two would be make a new tab to mount to something else.
I see Two potential problems with your "fix". One, Unless you ground quite a taper/step on the hole (and maybe you did just that) in the transmission I cant see it being below the mating surface. Bolting up the trans, tightening the bolts on either side, even if that nut is only a few thousandths high could lead to problems. Maybe not the day you tighten them...maybe never but still not a fan.
Reason #2, After some time of heat, vibration ect. if/when you go to remove the dip stick you may be hating life trying to figure what to do with that spinning nut thats loose down behind the engine. My Two Cents, Lorne

By the way, At 16 I had a '76 Camper Special that exact paint scheme. HaHa