$1650 is pretty good, I paid $2000 for mine and from the photos, I don't think mine is in as good of shape. At least being a CA car, like yours, there's no rust. I just did the front brakes on it and it is nice not having any rusted/frozen bolts on a 17 year old car.
I'm pretty sure you'd have to modify the seat rails for the Del Sol seats. From what I've read on the CRX forums to find out, the Del Sol seats are the ones people there are trying to get. Also heard of them being swapped into Integras because they apparently are as comfortable as integra seats, but you sit about 1 to 1 1/2 inches lower then the Integra seats.
From what I've read on CRX forums, you'd have to modify the CRX Si seat rails.
I wouldn't recommend the Ebay seats for about $250 only because of safety factors. A car seat has to support you in a rear end accident or you can break your back. I would trust one of the major car manufactures to have tested their seats not to fold up alot more then some no name Ebay brand.
Here's a thread on how to install Prelude seats into a CRX.
http://www.cardomain.com/ride/327027/9