Yes, I reckon it is Viso I, Ploot was never m mount. Having said that there are various 'scientific' or 'specialist' versions to confuse the issue.
I reckon it would be cheaper to find another that is LTM than to carry out a conversion. LTM PLOOTs and Viso Is are not expensive. LTM Viso IIs are harder to come by.
Remember, if you are going to use the system as originally designed the depth of the housing is important and changes from Viso I to Viso II.
All good fun though!