trying to repair a bad header block

Hi all. I've seen this searching in google. After a select on a table, i
got this:
ERROR: invalid page header in block 399 of relation "xxx"

I read about a tool called pg_filedump, and after some searchs about its
usage, i execute
pg_filedump $PG_DATA/base/xx/1234 (1234 is the oid of table xxx)

As expected, i found the "Invalid header information" in block 399.
Lots of this things inside:
Block  399 ********************************************************
<Header> -----Block Offset: 0x0031e000         Offsets: Lower    1663 (0x067f)Block: Size    0  Version   95
Upper      0 (0x0000)LSN:  logid 5714531 recoff 0x000000e0      Special  60660 (0xecf4)Items:  410
FreeSpace: 4294965633Length (including item array): 1660
 
Error: Invalid header information.

<Data> ------Item   1 -- Length:    0  Offset: 2600 (0x0a28)  Flags: 0x00Item   2 -- Length:    0  Offset:    0
(0x0000) Flags: 0x00Item   3 -- Length:    0  Offset:    0 (0x0000)  Flags: 0x00Item   4 -- Length:    0  Offset:    0
(0x0000) Flags: 0x00Item   5 -- Length: 32767  Offset: 32767 (0x7fff)  Flags: USED Error: Item contents extend beyond
block.       BlockSize<8192> Bytes Read<8192> Item Start<65534>.
 

This for several items.
Im triyng to 'repair' those items in any way, so i can dump the database
and analyze the hardware.

There is a way to 'correct' or blank the values somehow? I guess im going
to lose some data, iisnt...

Any hints?

Gerardo