This is just a reference post for some future searcher who can't find pistons for his HF or converting an old civic to a civic HF
As they are not making parts for HF CRX blocks anymore, when I had my engine rebuilt a year ago we used a JDM DX shortblock. This is the PM-8 head like a 92 civic CX or a CRX HF, and the DX block they used with the CX. Yes they used 4 valve relief pistons with a 2 valve for cylinder head on those CXs. The extra unused valve reliefs just cause it to lose a little compression.
The car is a 88 HF with stock MPFI fuel injection and A/C. It has 175 PSI compression. If stock it would have 185 PSI. It has a CA 3.25 HF transmission but with the federal ecu.
As compared to my friends '88 HF he bought brand new in '88 it seems to perform exactly the same MPG wise.
The thing that brings my average down from that is 24 cold commutes to work per tank for only .7 miles each way.
1992 CX head if the HF head is too warped and a used one is unavailable. Use the cam from the HF though. That's what I ended up with. They are both the PM-8 casting the CX has a different cam
88-91 JDM D15B2 shortblock. Just buy the whole thing for $400 and pull the head off it