a few questions for you itr guys, i did searches didnt find what i was looking for

1) how much na whp will the bottom end support for a daily driver while being reliable. jdm spec

2) when getting a head built do you guys use the one from your car or try to buy one thats broken? Any problems with buying 1 that has bad valves ect, when they are going to be replaced in the first place? Is there anyplace that sells basically just the empty shell of a type r head? Basically im going to be getting some headwork and was wondering if you guys buy a diff head or use your current. My current head is in perfect condition, only like 18k miles on it id rather not have it torn down and beefed up but im not gonna lose money over it by buying a head with a bad valve to find out its completely worthless and has been milled to **** or warped