Yes, this.
‘73+ F/M/J/B/R spindles are the same dimensionally.
The B/R casting are different, but the dimensions are the same. The FMJ spindles are a little lighter.
The steering arms between the B/R bodies and the FMJ’s are NOT the same, just FYI. The lengths are actually different, so if you’re using those steering arms you need the B body ones.