I have installed the Bravura in the 1983 Excella.
Huge difference! it is like a normal size elongated bowl.
Plenty of "tuck" room if you get my meaning.
You can actually get a cheaper brand that sits higher and has a bigger bowl. The drawback is that you may have to get adapter to fit to flange.
They sell them on EBAY all the time for around 79 dollars.
The Bravura by Thetford, fits right to your flange and typically cost close to 200 dollars but well worth the price. You can buy the elevator adaptor for a few more dollars to raise it nice and high for you leaners, squaters should have no problem with the standard setup