The oil return out of a turbo MUST point down. It comes out as a thick froth and if you have any restriction between turbo and sump you will have smoking issues. You can rotate the turbine and compressor on the core to point whichever way you need though.
I feel a CT26 will be on the too big side. I think EVOSti ran one on his 4A a while ago and he may have some better idea. They are also older and not as efficient as the new generation turbos.
Plus keep in mind that the bottom end of your silvertop will be identical to an AE101 GZE once you drop some ZE pistons in. Also check valve cleearances given the 4 flycuts in the piston and 5 valves. I *think* it all works fine, but may become an interference engine.
I think you are on the right track though.
Hen