Make sure the 292 will bore safely to .060 over 312. Have the cylinder walls sonic checked.
1) I don't know about trend lifters, but I'll comment on the pushrod part. One detail that most people don't do is to correct rocker geometry. Do a search here, Google it, there's all kinds of info about that. What it boils down to is assuming the geometry was correct to begin with (it's not) the bigger cam, head / block milling, valve job and other stuff I may not be thinking of at the moment make it so that you have to change the geometry to get it back to optimum. This inevitably means that you need different pushrods because the length requirement will be different. There are only 2 lengths of Y block pushrods available off the shelf so unless you are fortunate and one of those happens to be just what you need, you really need custom pushrods and since they are custom, you can have them made to fit any ball and cup arrangement you need. Even if you don't correct geometry, custom pushrods are not that expensive, $100-$120. And I'm sure comp will have good lifters to go with their cams, and if not, there's Isky, and Mummert.
2) Comparing MSD and Pertronix, in the case of the Y, anyway, is apples and oranges. Pertronix is only a conversion for stock distributors, from points to electronic. MSD is a complete, totally brand new distributor. So that is where a big part of the difference in cost is. You will still save money if you go with a rebuilt distributor and the pertronix conversion, and that should make for a pretty solid ignition. The MSD will be easier to tune because you don't have to take the distributor apart to get to the weights and springs and there is value in that.
The later distributor you have, have it rebuilt if you have not already.
3) I'd probably go with the 268 as well. I think with either, you are going to have to change the rear gear ratio. You'll also need to get the compression up. The heads and displacement increase will get that to a reasonably good spot, but those cams might like a little more and you'll need domed pistons to do that. With the G heads, 0 deck and composition head gaskets you'll be at about 9.35:1 With the 113s you'll be at about 9.04:1. Don't be afraid of premium fuel. You're going to kick the efficiency up enough that you might actually get better mileage than you do now (no promises) but also, bigger cams simply need more compression.
Lawrenceville, GA