Yes i actually forgot about the 125 rod - you can get them on the net , same as the crm125 .
If it was me with those barrels i would go straight to 180 or 190 kit because 308 is too much of a headache when you can get all the 300 stuff off the shelf .
The DR is a very busy man and if he agrees to do your pipes you have to be prepared to wait and he needs the rolling chassis too as he makes the pipes on the bike .
Can you put some photo's of those barrels up ?

If you do go the whole way and bore out those barrels i am sure you could get very simaler results as the rz400 i posted about . That would be expensive to get there but it will pull
like a tractor .
Let us know how it goes cos i am liking the idea of having a 380cc NSR !