not "knocking" the race engine builders mentioned[far from it and excuse the pun] but a cvh is a fairly simple -old school engine and any decent engine place should be able to rebuild one-as should a skilled diy enthusiast
i wouldnt pay a tuners labour rate for what is a routine job in all honesty...

high power yb,4g63,skyline,rx7 -yes... cvh for a nice xr2-no