Nice, bike, and welcome to the forum.

1986 was the stand-alone "Ironman" designation, but we're all masters and experts here!
The red/white was also offered in 1987 on the Ironman Expert model, but with those coppery Araya rims and 600 group, you've got an '86.
It should have Nitto bars/stem, fluted seatpost with a Turbo saddle. Group is 2x6 Shimano 600 SiS indexed, with great wheels.
The Tange 1 frame is a beauty, and the paint job cleans up very well. The red can be matched pretty close with Testor's red paint pens.
The white often fades a bit to more of a cream, mainly due to the clear coat over time. Whitewall cleaner scrubbing (and quick rinsing) brings it out some.

The others here are right, you can easily add a wider range freewheel, Kanegon has a couple of Centurions, knows his stuff, as do the others here. The suggestion for a 39t small front ring is very good. If you do both, at very reasonable expense, you've got a better climber, and it will be noticeable. There is an ISO/Trade thread here on the C&V forum, and you could offer to trade your freewheel and 42t ring for a larger freewheel and a 39t. You may have to put in a little cash, but it's cheaper than buying both.

I have three questions:
1. Is this possible considering the design of the original hub design?
Yes. Eventually, you could even go to 7-sp with a freewheel and shifter change.
2. Will it really make a noticeable difference?
Yes. As an ex-runner, you're inclined to "mash" at low rpm's. Almost any change, for climbing, is good.
3. Any other ideas, without making major adjustments or replacements?
White saddle, white wrap, white housings? Purely for appearance. Clipless pedals.

thank you so much...i am new to this world but consider myself very handy
You're welcome here.