I dont own a first gen CRX but Ive seen a few people who have converted them to MPFI. Not sure how they did that but its better than the carbed version. There are also headers and exhaust systems available. Im not sure from who but I remember back in the day DC sports had a header, not sure if they still do.
If you are lucky once in a blue moon on eBay Mugen parts will come up for those motors. Like header systems, exhausts, even suspension. But be prepared to pay out the nose for them. The last 1st gen thing I saw from Mugen for sale on eBay was a valve cover that went for about $1100 US.
CRX Forum