Here's the deal.
The sole purpose of that bracket, other than something to mount the heat shield to, is too help relieve the weight of the turbo on the header. Without the J bracket, the full weight of the turbo is out there bouncing around when the header starts to get hot, starts to glow cherry red under WOT and pliable. Eventually, this will heat fatigue the headers, especially if stock, you will see cracks start to form around the bulges/folds of the main tube and where the primary tubes are welded to the main tube. I have been screaming it for years, as I've seen a bunch of cars with a cracked passengers side header caused by not running the stock heat shield, "J" bracket. Cars that are not driven often, or only raced and put back in the garage will definitely take a lot longer to crack the header. But a street car that get's abused weekly / monthly will crack a lot sooner. So, IMHO, for longevities sake, you gotta run that bracket.
More food for thought, stock headers can be upwards of 34 years old if they are from an early "86 model. Typically produced in late "85 for the "86 models is not uncommon. And we all know the steel used, was barely passable back when they were new. If you choose not to run a turbo heat shield, at least do something to fab up a similar bracket, or alter the stock one so that the turbo's weight is still supported. No matter which headers you run.... they will absolutely love you for running any type of turbo bracket. It was the very first thing I put back on my current car when I got it and all 4 of mine have had the stock bracket. Pic attached are some of the weak spots on the stock header that I've seen crack before.
View attachment 336518
Just my O2's worth.
-Patrick-