Help with Strike Plate Mortise

[sbattisti]

OK, so, I'm not terribly handy, for starters. I'm working on installing some new doorknobs, and I've found that the mortise where the old strike plate was is very different from the new strike plate. I can chisel out some wood at the top to raise the strike plate to where I need it, but then I will have two problems:

1. After I install the strike plate, there will be an ugly, empty space below the strike plate.
2. The lower screw will likely align right where the old hole for the latch assembly goes.

I've tried watching YouTube videos, but they mostly seem to be focused on things that aren't quite a match for my scenario. It's very frustrating. I can't figure out how to fill in the gap (#1 above) and what to do about #2 so that the screw will have somewhere to catch.

Do I need to cut out the whole section and repair it with a block of wood and start over? Or fill the whole thing with some kind of putty or something?

Advice greatly appreciated.