Definately FTW.
I changed the whole rear subframe on my Datsun for Solid Rear axle to F.IRS. Holy Shit it make a HUGE difference in how it drove. It was well worth the week of all nighters to line that thing up and weld the IRS subframe in.
All it really needed to be perfect was a larger rear sway bar. The stock one on there literally looks like a A bunch of paper clips straightened out and welded at the ends to make it longer. I guess it helped that the car was so light so there wasn’t any opportunity for roll anyway.