I would try the toolholders linked to by the OP (Only 4 off available now though).
I bought my original toolholders and QCTP set from A&R Precision and find I can use 10mm tooling easily on my ML7.
Since then I've bought the SOBA toolholders from Chronos and toolholders from Myford and these have a thicker lower shelf. I can just about use 3/8" tooling in the Myford ones but can confirm your findings about the Soba ones andthey are now only used for boring bars with lower cutting edges.
I'll try and find the original threads where this issue was discussed.
http://www.model-engineer.co.uk/forums/postings.asp?th=82603&p=1
http://www.model-engineer.co.uk/forums/postings.asp?th=104291
http://www.model-engineer.co.uk/forums/postings.asp?th=80916&p=1
HTH
Jon
Edited By Jon Gibbs on 22/06/2016 13:21:27
Edited By Jon Gibbs on 22/06/2016 13:23:10
Edited By Jon Gibbs on 22/06/2016 13:24:32