Nice work Gabe, congratulations.
Historically there weren't so many single-ended EL34 amps on the market. The exception, perhaps, was the Pye HF10 from the company's 'Mozart' range. I've never worked on one of those but they claimed that it could deliver 10W from one EL34 and that it had just 0.3% THD at 9W output ! The circuit (given here
https://www.valve-radio.co.uk/litera...-instructions/ for example) was unusual and I suspect the output transformer may have been fairly special too.
The one thing I'd say, and you may already have done this already, is that if you're going to hand it over to your sister-in-law then you might want to put a baseplate on it. Otherwise sooner or later someone inexperienced will try to pick it up while it's still plugged into the mains. If their fingers should touch mains live and either earth or neutral at the same time they will get an unwelcome shock. At the least they might drop the amp onto their foot which won't be good either for the amp or for their foot.
EDIT: This post crossed with your second one, so I see you do have a baseplate.
Cheers,
GJ