There were a number of mixed-propulsion projects ...
Aye, but the 'screech looks like a "proper "1950s jet only with a prop. up front rather than the, interesting, oddballs that you've noted that look, in the main, like standard piston engine airframes. It should also be possible to find good three-views of the 'screech's donor airframe well, which may be a bit more of a problem with at least some of the others. The airframe is also quite conventional in plan so it's likely to be susceptible to the usual trimming techniques for rubber powered models.
... prop-driven tail-sitter projects of the early 1950s:
Beyond, way beyond, my aeromodelling talents I think. Can't for the life of me see how you'd even begin trim one of these for rubber powered freeflight. You might
just be able to get a ROG - the torque effect of an unwinding motor without the equivalent of a helicopter tail rotor would be "interesting" - but I can't see how you'd transition to level flight. Think that the flight profile would be, "Corkscrew up, 'hang' for a second or three in mid-air until power out then fall straight back to earth creating a pile of splinters and tissue on contact." Or possibly a corkscrew parabola with impact under power. Nooo. An experiment for some-one braver than me I think.
Suspect the only practical solution for a tail sitter would be to gut a cheap multi-rotor drone for its gyro(s)* and motor(s) and go the RC route and even then I still can't see how you'd transition to level flight.
*Or accelerometer/whatever they use for stabilization.
Perhaps this discussion should be continued - if necessary - on pub/flights of fancy?