I'm far from an expert in general relativity, but I think your portal will have another property that you haven't considered: An extremely strong gravitational field. The field doesn't need to extend beyond the mouths of the wormhole; keeping it in the "throat" of the wormhole is fine; but it'll need to be there.
The way that wormholes are normally thought to work, time passes at the same rate on both sides, as seen by observers on either side of the wormhole.
That is, say I have two synchronized clocks.
I set one on a table by one mouth of the wormhole, then I pick up the other and carry it through the wormhole. I wait a bit on the other side of the wormhole, then I haul the clock back through. When I compare it to the first clock (still sitting on the table), they will still be perfectly synchronized. The second clock's trip through the wormhole won't cause its timekeeping to diverge from the first clock at all.
This holds even if the exit mouth of the wormhole is located on a spaceship zipping away from Earth at a significant fraction of the speed of light, and also if both mouths are on Earth but one is located thirty years in the past.
Your wormhole does not behave this way.
Say I repeated the experiment with the synchronized clocks, starting on the "present" side of your wormhole. I pick up one clock, step through to the past, wait thirty seconds, and return. Now, the clocks are out of sync. The clock I carried measured thirty seconds, while the clock that remained in the present measured only ten seconds. They're off by twenty seconds, relative to each other.
So... clearly there's some sort of time dilation going on.
The kinds of time dilation seen in special relativity don't help here. As mentioned earlier, "normal" wormholes don't desynchronize clocks, even if one of them is in a relativistic spaceship or orbiting a black hole.
You might be able to get this effect is the exit portal is accelerating extremely rapidly (i.e. on a spaceship that's burning a hideously powerful rocket engine, or sitting on the surface of a stellar remnant- the effect is the same)... but you've also specified that your exit portal is on Earth. So your wormhole must be doing something else.
Which leaves just one thing that I know of: Gravitational time dilation.
Time passes slower the deeper you are in a gravitational field.
According to that Wikipedia page, the Earth's core is about 2.5 years younger than its surface.
If you synchronized two very precise clocks at the Earth's core four billion years ago, shipped it up to the surface, waited until the present day, and brought it back down to your lair in the core, you'd find that the the clock that was on the surface is now 2.5 years ahead of the clock that stayed in the core.
That's the same result we got from when I took a clock into the past using your wormhole. The magnitude of the effect is different, but the effect is the same.
Therefore, your "past" portal must be "above" your present portal, with respect to travel through the wormhole.
Going to the past will require climbing against an extremely strong gravitational field. I don't know how strong precisely, and I imagine you could reduce the strength of the gravity if you make the wormhole very long. Either way, I hope you've brought a ladder. Or, better yet, a winch on the "past" side with a very strong cable.
Returning to the present would require going "down" through the same gravitational gradient. A parachute would help... if all the air in the wormhole weren't getting sucked through to the present with the same acceleration. Once again, a ladder (or a winch, or a fireman's pole, etc.) would probably be your best bet.
On that note, there would also be a great gale of wind rushing into the "past" side of the wormhole and out the "present" side. Watch out for falling debris. (Unless, of course, somebody built a vacuum chamber around the "past" side. In which case, you'll have to bring your own air when you climb the ladder.)
Looking into the portal from the "present" side would be like looking up from somewhere near a black hole. You're right that all the photons coming from the past would be all bunched together. They'd also be blueshifted quite a lot, probably well into the ultraviolet. (Bring sunglasses.) Infrared light might get shifted into the visible spectrum, enabling you to see heat without needing a fancy IR camera.
Also, if you look at the edges of the wormhole, you may see a lot of distorted reflections of your own face and of other things on the "present" side of the wormhole. Gravity does bend light, and the gravity in your wormhole is no exception.
Looking into the wormhole from the "past" side would be the opposite. Not a whole lot of light would make it through, and what does would be redshifted, probably well into the infrared. If the Sun is shining on the "present" side, some of the Sun's ultraviolet light may be shifted into the visible. Or maybe not, I'm not sure.
You may also see reflections of yourself and things behind you on the "past" side. It depends on the exact geometry of the wormhole, but they probably wouldn't be as prominent, and would be relegated to the edges of the wormhole more so than on the "present" side.
All in all, not a method I'd prefer to use in order to get to the past. I'll stick to my nice, well-behaved Ellis wormholes, thank you very much.