Had some discussion on this before, where I suggested deflecting the cam belt or chain to alter camshaft timing on the fly. Well, couldn't think of a good way to do it then, but just came up with a way that it might be achieved using some off the shelf, or wreckers yard parts.
First off, the mechanism of deflection, best achieved I think with two idlers fixed with respect to each other, on an arm that can be moved back and forward. One would be on the tooth side of the belt, the other on the smooth side, ahead and behind the camshaft. They'd be set up to be deflecting the belt equally at rest, then when the arm is moved, tension is released on one side as it it taken up on the other, keeping constant stock belt tension. In this way, the system is somewhat failsafe in that if the actuator fails the belt should not jump, cam may be left advanced or retarded, but should run still until you fix it, unless you went really wild.
So with the idlers neutral, you'd set up your base cam timing. Probably want it advanced for lower down torque, with the adjustment going towards retarded for top end power.
Now, how do we move it? Well I was first thinking solenoids, but not expecting them to have the power, or be easy to control if powerful. I didn't think of hydraulics, until I heard it mentioned that limited hydraulics could be driven off the power steering pump. So I started thinking how to control that..... and I remembered that fuel pressure regulators are often vacuum controlled, AHA!!! So, if we get a suitable FPR, we can use vacuum to bias a hydraulic actuator to move the idlers back and forward. Set it up for low down torque and good economy at high vacuum and high end power at low vacuum! Would take some fiddling with to get it set nice I'd think, and would need other adjustment valves and probably an AFPR, but apart from the linkages and the idler arm, I think you can round up pretty much everything you need to do it.
So, might try this on the Escort eventually, which has known sweet spots for the cam timing, and should also remain non-interference in case I screw up, whereas the van's new motor is going to be interference, so want to have experience with it before I do it to that.
Might need to figure out how to bias ignition advance and retard though, since that will change WRT TDC if timed off the cam.