Extending hearth extension?

[Ctwoodtick]

going to be switching from carpet to hardwood flooring sometime in near future. Currently have a Jotul Rockland in masonry chimney. We have 18 inches of hearth extension. I have often thought about having a small free standing stove in firebox of masonry chimney instead or if any costly repairs were ever needed to existing insert. I would like to use current insulated ss liner used for insert. Good block off plate needed as well of course.
Couple questions- first, existing firebox is 31 inches high. Would any small stoves fit in that area? The current insert is in a room that is roughly 20x15. Gets pretty toasty in there already/ not sure if free standing stove would cook us right out or not, or perhaps the difference would be minimal.
Secondly, i am wondering if the best time to add any needed hearth extension would be before new flop goes down. What would you all expect the cost of this to be to add let’s say 4 or 5 inches to extension?

 

[begreen]

A Hampton H300 would fit in there. It's 30.25" to the top of the flue collar or 24.75" with the short leg option.

 

[Ctwoodtick]

Would there be a benefit to having a free standing stove like this extending at least partly onto hearth? With new hardwood flooring going in within next year, I’d like to add stone to extend hearth extension (to meet minimum clearances) before floor installation. I imagine the stove being partly in old fireplace opening and partly outside of it might be an option. If so, would use of a “T” connection come in?