A 1000+ hp car with an aftermarket cam (more so if it's high stage) and a bunch of other fixings have always been niche. To some people it's a sign the car has been beat to hell to others it's about trusting a shop you don't know. If you haven't, I would list the shop that did the work, along with a little bit about them.
Even 15+ years ago people were getting 20% on the dollar for the cost of the mods, not counting install and tuning. I remember seeing a decent amount of heavy modded Zo6, Grand Sports, and even Base models sitting for sale for a long time, when people wanted to factor in the cost of the mods too heavily. When the price starts to creep up too much you're competing against "Well I can buy a new(er) car and pay for mods later" or "why not just buy a ZR1" when it comes to most people in the market.
That said, it sounds like you have time, you just need to find the right buyer out of a very small pool of people that are not only interested, also have the ability to buy it. It might take a year though.