I don’t know if the English of plans set is not as up to date as the French set.
A very interesting source of information is the “GPPA” of the Angers aviation museum (see link below)http://www.musee-aviation-angers.fr/las ... on-avions/
For 150 € (+ shipment) they can send you a CD full of plans scans.
You could use the “Piel CP-301 Emeraude & dérivés” set of plans, that contains the plans of different versions of the Emeraude and other derived Piel planes from the first CP301…
About the engine, the CP320 can be fitted with any good old O-235, O-290, O-320 or IO-320 Lycoming engine, but as far as I know, there is no IO-235. (Just a recent and lighter IO-233… with a computerized electronic injection system and FADEC, that I fear to be much less affordable).
But whatever engine you will chose, the best thing to do will be to fit it with a tuned exhaust.