Hey Fluffy Cat - if by the JhA triple you mean part number C10054-00 on their website, the answer is yes, RVF forks will work - below is a copy of an email from JhA asking them that exact question. Respondent's email is sasaki@jha.co.jp if you want to follow-up.

"Dear Sir.

Thank you very much for your inquiry about our product. The upside-down
forks of RVF400 can be installed as it is in the stem set which the parts
number is C10054-00.

If you have more questions, don't hesitate to contact us.

Best Regards,

Makiko Honda ( Writer of this mail on behalf of M. Honda is A. Sasaki.)
Jha Racing Sales Dept."

Me again - For anyone interested, I followed up asking them if rs250 forks would work with the same triples and they basically said they don't know. Their response:

"Dear Sir.

Thank you very much for your inquiry about our product.

We regret to say that we don't have experience that we install RS250 forks
with the stem set and take the bike to dyno and also do the real running
test with the bike which the forks are installed. So, we don't know whether
the problem occur with this combination or not. Therefore we don't know
whether RS250 forks can be installed with the stem set in terms of
performance and also in terms of dimensions, or not.


Best Regards,

Makiko Honda ( Writer of this mail on behalf of M. Honda is A. Sasaki.)
Jha Racing Sales Dept."

Hope that helps.
_________________
-Jim
'93 MC21