Hi Lewm,
If you want to keep the characters of the Koetsu, I caution you on using aftermarket retippers, especially VDH!
Just to share my experience, about 20 years ago, I bought a used FR64S and the seller also sent me a vintage long body Koetsu rosewood without the cantilever. Not knowing whether I would like the Koetsu sound at the time, I opted to send the rosewood to VDH, instead of Koetsu, for retipping. The returned cartridge worked and sounded fine, but it didn't have the famous "warm" sounding which Koetsu cartridges were known for.
A few years later, my friend loaned me a, then current, Koetsu rosewood for comparison. This newer rosewood sounded a lot warmer than mine. So, I am pretty sure the retip by VDH did change the character of the rosewood, more like in between a Koetsu and a VDH. Personally, I liked the VDH retipped rosewood better, but if you are looking to keep the Koetsu character, the VDH retip probably would not fit you.
Bests,