I would probably recommend that route too but I already got BBP rear axles installed on my 7.25 rear end. It’s also a slant 6 car and I’m keeping it that way.
You shouldn't have any issues if you want to run the spacers. 1.5" seems like a lot but compared to the 4x4 crowd its not all that big, and they tend to run way bigger tires and higher wheel mass. Thinner spacers are actually more fragile as they've got less material to hold the second set of studs. Biggest thing is just to make sure that you check the torque on BOTH sets of lug nuts, somewhat frequently at first especially.
I run a '68-70 B body 8 3/4 in my Duster, it's not a bad way to go as they're a bit cheaper than the A-body version but it really depends on the wheels you want. I have 18x10's with a +38 offset (7" backspace) on mine with 295's, but I also have the springs offset a 1/2". With wheels less than 9" wide it's pretty easy to find the higher offsets for the wider 8 3/4. Once you get to 10" or more it seems the offsets all drop down, I've considered putting an A-body width 8 3/4 back in my Duster so I can run 18x11's with a +15 ish offset as that's a more popular offset for that width.