Stored Procedures - String split stored procedure

I have a nvarchar field. The field has spaces in no particlar format. I have used replace function to get rid of the spaces & to get a continuous string.

But I need to take its last 3 characters and insert a space between first n characters & last 3

So if the string is ABCDEFG-I want ABCD EFG
if the string is ABCDEFGH-I want ABCDE FGH etc

How do i write a stored procedure to do this

SELECT
CASE WHEN LEN(column) > 3 THEN
SUBSTRING(column,1,LEN(column)-3) + ' ' + SUBSTRING(column,LEN(column)-2,3))
ELSE 'Too short'
END
FROM table