how much does N42 head cost..if just out of an running engine??

how much should i pay...hes asking for $250

You could probably get one out of an engine that wasn't just running for $100 or $150. The question should be how many miles are on it. If it needs a valve job because it has 80K miles, you might as well start with a cheaper one.

its has 160k miles on them..compare to P90 which is better/performance/easier to modify..and which block (N42 or F54) should i use..

will be running SU's from Ztheraphy..plus is it a good idea to use my '73 240z crank and rods to L28 block..to maintain a hi-reving engine like the 240's???

Those are some big questions. I would suggest you take some time and search and read, search and read. And when you've done that for about a week, do a little more searching and reading. Try searching hybridz.org too. Lots of good info about heads over there.

$250 for a head with 160K on it is too much in my opinion.

Where would you get the pistons to make that combo work? There is a 5.3 mm difference in stroke as well as a 3 mm bore difference between the two engines. Jon is right...you need more research.

that's what i though a little too much..will make an offer for $100..

yah.. i need to do more research..

Don't forget about the bronze valve seats depending on what year it came out of.

it came out of 1976..they said the block N42 also is good to use on stroker motor..due to thicker better metal than F54

That's true.