A 1:45 pace for 800m is again, pretty good for distance swimming, though not as competitive as your 1:09 sprint speed. But do keep in mind you are working at two very different demands here with an 800m vs. a 100m race. You won't be able to achieve optimal times for both events at the same time.
A large part of gaining speed with TI methods is to learn to increase your stroke rate while keeping your stroke long. A Finis Tempo Trainer is extremely helpful for this. You might look at Terry's postings on ways to use a Tempo Trainer:
But first, are you familiar with the TI green zone chart? If not, read this:
If you are not already in your green zone (based on your "wingspan" of outstretched arms), I'd suggest prioritizing your training to lengthen your stroke until you are. Swimming at high SPL (strokes per length) is an indicator of fundamental inefficiency in balance and streamline.
Based on your height (not as accurate as you wingspan), you should be using between 17-21 strokes to cross a 25m pool--if you use a standard 5m pushoff at the wall.
So, that should give you some idea how to train. If you can swim comfortably at speed at 17 SPL, your mechanics are pretty good. In that case, you would probably benefit most from Tempo Trainer work to increase your stroke rate while keeping your stroke long.
If you are taking more than 21 strokes to cross the pool at speed, then work on drills and slow, short repeats (25m, say) to increase the length of your stroke. A good TI swimmer should be able to choose any SPL (strokes per length) within his green zone at will, and will then play with SPL and stroke rate to adjust speed and perceived effort for any given distance and pace.
Hope some of that is helpful--you do have enough time to make significant progress in technique, but be patient with it. Good luck, and keep us posted on how your training progresses. (I agree with Werner that Coach Mat's materials are EXCELLENT, as is his blog (linked above).