Any drawback to keeping the drum spindles on my 66 Valiant?

Yeah the Wilwoods won’t work with any of the original SBP wheels. Or even those police wheels.

I think Leeds picked up where SSBC left off, that would be an option. Obviously the drawback there is the company went out of business once already. But most of the wearing parts are just mustang parts. The rotors are modified but with the number of miles most people drive these cars one set of rotors might be all you need anyway. Maybe two?

All the 73+ mopar disks widen the track the same amount, the 10.95’s and 11.75’s are the same there. Both would make them wider than it is now with the 10” drum spindles. But the hub on those would be too big for your original wheels. They would work fine with the police wheels though.

You could also look at scarebird, they have kits for the 10” drum spindles. I don’t know a ton about those conversions other than they use Toyota rotors but I know some of the earlier rims fit. You’d have to have the SBP drilled into the hub though.

There’s also the MBM kit, it’s just a 73+ mopar disk set up but they turn down the hub some so the earlier mopar disk wheels fit (not enough meat to take out for the drum wheels) and have the rotor blank drilled for SBP. You could have those mods done at you your local machine shop. I thought DoctorDiff mentioned somewhere about doing something similar, maybe that was a rear disk set up.