Student solo privilege in the phase one, is found in the FAA generated Operating Limitations issued with the Airworthiness Certificate. (as I pasted in an earlier post)
The FAA Certificated prop and engine combination requires the the correct certificated prop is approved for the engine in the Type Certificate Data Sheets (TCDS) The trick is the engine and prop must still meet the FAA TCDS. Only FAA approved modifications are allowed on the prop and engine In Accordance With the FAA Supplemental type certificate (STC) All Airworthiness Directives (ADs) must be complied with for the combination to be approved.
No (unapproved) modifications are allowed to ignition systems, fuel systems, exhaust system, etc. In my 20 years as a DAR, I have never been able to approve the engine / prop combo for a shorter time in phase 1. Expanding the phase one test are is a much easier chore and I have never yet had one rejected.
Another cool tip is; The radius center of the phase one area may be defined by any point on a sectional chart. In the Chicago area we have Lake Michigan and class B & C airspace to deal with. Flying over Lake Michigan is approved for phase one, but I have yet to find anyone willing to do it. You can center on a small town, lake, intersection (VFR, highway or river) radio tower, etc. Your home airport has to be located within the circle.