wah, 400,000! Mine only 200,000 only, and it's due for overhaul already.. actually no, if it werent for the piston 1 valve leak. :P
Well, overhauling usually isn't as cheap as you think because new parts will cost s a lot more than used. esp. for certain items like rocker arms, tappets, etc, which can easily eclipse the price of a used PR-3 head.
in fact, some people simply buy another B16A engine kosong rather than fix, because it's cheaper, esp. if the original engine has too much worn parts.
To check your engine health, usually good mechanics can check visually for oil leaks and then do a compression/leakdown test to see if there's air leaks. sometimes just hearing the noise made can give clues already.
I only know Seong VTEC, Bkt. Kemuning Shah Alam, and LoChi, USJ1 Subang. Both knows VTEC engines because they work on them a lot. There's others, but I don't know them that well.
Good luck though, but remember that new parts will kill your budget pretty quickly at 2-3K. but if you just need to change seals, piston ring, valve grind and gasket, probably no.
RAM, welcome to ZTH.