>     puc0 at pci0 dev 11 function 0: Dolphin Peripherals 4036 (com, com)
>     com3 at puc0 port 0: interrupting at irq 10
>     com3: ns16550a, working fifo
>     com4 at puc0 port 1: interrupting at irq 10
>     com4: ns16550a, working fifo
>
> It doesn't quite work though.  A 4800 baud stream injected into the
> port prints out garbage at what looks like a ~110 baud.  Shades of
> paper tty days. ;-)

looks like the manufacturer made new product without changing PCI id.

as of you write it's faster clocked version but in pucdata.c there's still
COM_FREQ put (=115200)

try replacing  COM_FREQ with maximum speed it can do in pucdata.c entry