I'm not convinced they are SD1446, even though they're labelled as RM SD1446.
As far as I'm aware, the SD1446 was obsoleted a while ago.
Furthermore, the SD1446 is capable of easily doing around 80W, so 4 x SD1446 would do 320W if pushed - but no more than ~240W will be achieved from the KL505.
I do wonder, though, if RM got a big batch of SD1446 rejects (low gain), hence why they're marked RM SD1446.
On another note, the schematic diagram provided with this KL505 says they're using 4 x SD1407 which are expensive 28V devices!