WOW! That is a really fantastic harness! Truly a pity it isn’t suitable for all your interests but it is an excellent harness for a majority of your interests and yet it not being entirely compatible for LH it does leave you an opportunity to expand your armor collection and represent another time period! 
Perhaps no shock, but I'll echo that "two sets of armor" idea.
As Sir Wolf said, the main thing with the cuirass is it is "inverted", under/over instead of over/under. I would call it "historically influenced". The arms are close, the elbow cops are close except should "flare out" towards the elbow in more of a "V". The knee cops don't strike me as historical though they may be based off of an uncommon example. There are lots of other odds and ends that put it "historically based" rather than "historical reproduction". I would say don't try to adapt it to Living History.
You'd essentially be looking at replacement of most plate parts. Spread it out over time, and it isn't too bad. If you are planning for Days of Knights, do "soft kit" this year and plan for "hard kit" in 2015. Buy something every 4 months; cuirass, arms, legs, helmet, gauntlets... that's 20 months and falls right about Oct next year, in time for DoK, if that is a reasonable timeframe for your budget.
And I say two harnesses because it is a great harness already. It is suitable for many purposes, and you would be essentially ruining a perfectly good harness to try to "convert" it to Living History - beyond that, it may be almost as expensive, or more, to do so, and you end up with only one harness still. You already have the requisite arming clothes and sword.
