I acquired a NA L28 ($50) with the F54 Block stamping and a P90A Head, the pistons were dished but it had a NA set of intake and exhaust manifolds.

Is this a turbo engine converted to NA or is it possible that Nissan produced F54/P90A combinations for non-turbo applications with dished pistons? Are the internals any different between NA and turbo in this combination?

My main concern is the pistons capabilities to withstand 8-12 pounds of boost.

With dished pistons and a P-90 head , you have a turbo engine with as for the amount of boost it will handel , for that you will need to ask a turbo guy , sorry. The P-90 is a low compression head and and is for use with a turbo . The F-54 block that has flat topped pistons is the same engine but higher compression and ment for injecton . It will have a P-79 head and it can also use carbs , the compression is higher because of the lack of any boost. I think 8.5 to 1 or about that. I am using a '82 flat top with a P-79 and SUs. Gary P.S. give phred a PM he is an engine builder and a member. He is the real deal and knows his stuff. I think the P-90 A is a head with hidrolic valve lifters . I know I miss spelled hidrolic. Dislexia is a hell of a thing.