landeck , any one of the engines you have listed would be adequate to power a Senior . I have built and flown many Senoirs over the years ,varying from stock threechannel to a highly modified flat wing, enlarged rudder, barndoor aileron - beast . No mater how you build it or power it will still fly . I prefer 4 strokes and usualy use an 80 or 91 saito. 4 strokes are quieter .
A 4 stroke won't make it to heavy and you won't have to add a bunch of tail weight or shorten the nose, just move your equiptment and batteries around to get the C.G where you want it .