Some very interesting info here, thanks.

The Walker catalog part fitment for the rear muffler hanger bracket is the same as RockAuto. Clearly the bracket seems to fit the muffler profile reasonably well, but the ears seem incorrect, seemingly too low set (making the muffler high) and they also look too short. I hope you make RockAuto aware of this fitment issue and even ask for a refund.

The Starla brackets, with their European plant now owned by Walker, are seemingly slightly different from the Walker branded ones. I've not had problems with the Starla brackets on the Starla rear mufflers, but did have to signficantly adjust the shape to properly wrap a Starla bracket around an old genuine Volvo muffler I tripped over on a shop closeout sale.

The genuine Volvo brackets are still available (for a hefty price), both the upper strap and the lower clamp (rod) bracket, which are sold separately. It's a very different design and may need significant bending to get it to properly fit the Starla rear muffler, which is presumably a very similar profile to the Walker. The upper band on the Volvo bracket rusts out easily, but the replacement cost of just that band can be more than that of a whole Starla bracket.

Mixing and matching these older muffler systems is obviously frought with risks. At the very least, you'd expect a Walker bracket to work with a Walker muffler in our 900s and even 700s (which have similar rear mounting).

I'm impresssed in your pics that you went with the original wrap style muffler pipe clamps, not the everyday U-bolt pipe clamps which can put a groove in the pipes that later makes them impossible to separate. The wrap clamps need to be used on slitted pipe joints, while the U-bolts may be needed on unslitted joints. I will often slit an outer pipe flange with my angle grinder to make for a better fit using a wrap clamp. What brand and where did you source those clamps? I don't see them on RockAuto.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now