Unless you are very skilled with fiberglass, it is both cost prohibitive, and probably a cosmetic issue. There are a fair number of the high top boats around. I wonder if the mold for the "hi Top Roof" was damaged or destroyed in the fire, and not rebuilt? My good friend had a high top, which sold last year...it took a long time to sell, even though it was a very good boat, cantilevered Bimini, and 115 Suzuki, with modest hours, well cared for...reason didn't sell, right away, was it was in Pensacola--would have sold in very short time the PNW.
The easiest way would be to just extend the very top, make the cut around the top, bring the sides, back and front up at the same angle, using waxed Masonite forms, to simulate a mold, then cut the edge of the old top to fit the slightly narrower profile. You may still have issues at the helm.
The better course is to get a 25 or a Tom Cat--the 25 I believe is about 6'10" head room. I am 6'2" and the standard C Dory has a couple of inches--the 25 has much more. My son is 6'4" and likes his 25 much better than the 22. The bunk is another issue. With the Tom Cat--you have a bunk which is over 7' long. For the 25 you can cut out the entire port side of the bulkhead between the V berth and main cabin. In my 25, (fiberglass interior, 1967), by cutting out this bulkhead, you gain over a foot in bunk length (just make a cushion--or a storage box, and a cushion) in the forward facing foot well, and you have plenty of room for sleeping. With the 22, sleeping may be an issue.
You have to duck going thru the door in any of these--a 7 foot door, would be very expensive from Diamond Sea Glaze.