While I sorting blocks by group, I found:
this block not exist in SMBX item panel:
You can check yourself:
(Full blocks panel sheet)
I made dummy level with already placed 183th block and open them via SMBX:
Bit then I drag them, it will transform to 1st block, I.e. famous wood block:
I think, you never turned attention to them, while you looking for your necessary block in graphics folder
You can get my dummy level and check yourself:
http://engine.wohlnet.ru/docs/_files_fo ... ck-183.lvl
Simply drag placed block, and you will see