I did some additional hack and now notice some errors which strangely does not stop the system from functioning but needs fixing;
The 'Block Type' drop list on the Add new block form starts with 'Side Block - Left and I moved Center Block - Center to that position so it now looks like this and fuctions correctly;
Center Block - Center
Side Block - Left
Side Block - Right
Center Block - Left
Center Block - Right
I edited files;
include/common.php
 [color=CC0000] define("XOOPS_CENTERBLOCK_CENTER",0); 
    define("XOOPS_SIDEBLOCK_LEFT",1); 
    define("XOOPS_SIDEBLOCK_RIGHT",2); 
    define("XOOPS_SIDEBLOCK_BOTH",3);[/color] 
    define("XOOPS_CENTERBLOCK_LEFT",4); 
    define("XOOPS_CENTERBLOCK_RIGHT",5); 
    define("XOOPS_CENTERBLOCK_ALL",6); 
 [color=CC0000]  /* define("XOOPS_CENTERBLOCK_BOTTOMLEFT",7); */ 
   /* define("XOOPS_CENTERBLOCK_BOTTOMRIGHT",8); */ 
   /* define("XOOPS_CENTERBLOCK_BOTTOM",9); */ [/color] 
    define("XOOPS_BLOCK_INVISIBLE",0); 
    define("XOOPS_BLOCK_VISIBLE",1); 
    define("XOOPS_MATCH_START",0); 
    define("XOOPS_MATCH_END",1); 
    define("XOOPS_MATCH_EQUAL",2); 
    define("XOOPS_MATCH_CONTAIN",3); 
    define("SMARTY_DIR", XOOPS_ROOT_PATH."/class/smarty/"); 
    define("XOOPS_CACHE_PATH", XOOPS_ROOT_PATH."/cache"); 
    define("XOOPS_UPLOAD_PATH", XOOPS_ROOT_PATH."/uploads"); 
    define("XOOPS_THEME_PATH", XOOPS_ROOT_PATH."/themes"); 
    define("XOOPS_COMPILE_PATH", XOOPS_ROOT_PATH."/templates_c"); 
    define("XOOPS_THEME_URL", XOOPS_URL."/themes"); 
    define("XOOPS_UPLOAD_URL", XOOPS_URL."/uploads");  
modules/system/admin/blocksadmin/blockform.php
 $side_select = new XoopsFormSelect(_AM_BLKTYPE, "bside", $block['side']); 
$side_select->addOptionArray(array(0 => [color=CC0000]_AM_CBCENTER, 1 => _AM_SBLEFT, 3 => _AM_SBRIGHT, 4 => _AM_CBLEFT, 5 => _AM_CBRIGHT,[/color] ));  
The errors are
1. When I upload the changed files all the existing blocks switch positions.
 - Center blocks move to the right
 - right blocks move to the left
 - Left blocks move to the center
When I switch them to the correct positions with the radio select they stay and display properly.
2. In the Groups settings;
 - No center blocks show. Just the title 'Center'
 - All the center blocks show in the right list (though they display correctly on the pages)
 - Left block list display correct but they also duplicate in the right list (These also show correctly on the pages)

The blocksadmin list shows all blocks in their correct position.
I looked at files in modules/system/admin/groups but didn't see any obvious line to edit. It is probably there but I don't know how to interpret it.
Can anyone assist with this? Thanks.