Spindles? We'll pretend you mean axles. No BBP replacement axles are available for the early 7.25 that I've ever heard of. Adapters are your only option to go BBP with the early ('72 and earlier) 7.25. Other differential options are the '73 and later 7.25 (no, the axles don't interchange between early and late diffs), the A body 8.25 (offered '73-'76), the 8.75 (which will still require aftermarket 4.5 bc axles and B/C/E body brake assemblies), or a narrowed Dana 60.
A non-Mopar option is the Ford 8.8" rear out of an Explorer. Do a search in the Drivetrain forum for more info on this setup.