Am I right in thinking the following link is the full version of IVA manual? I remember the SVA manual had to be purchased?

link to manual

Yes.

Just be careful with direct links to the pdf as they might call later versions different file names - not sure what they do tbh.
If in doubt, go to the hosting page instead then you're sure of getting the right one

https://www.gov.uk/government/publications/iva-manual-for-vehicle-category-m1

The latest manual is linked and fairly regularly updated in the sticky at the top of this section.