LetterContent.LetterStyle (Word)

Returns or sets the layout of a letter created by the Letter Wizard. Possible return values are wdFullBlock - Full block, wdModifiedBlock - Modified block, wdSemiBlock - Semi-block.

Set aLetterContent = New LetterContent 
aLetterContent.LetterStyle = wdFullBlock 
ActiveDocument.RunLetterWizard _ 
 LetterContent:=aLetterContent, WizardMode:=True