1973 Dart H Code value

Why do you want it?
If it’s to make yourself a fun car then $1000 or maybe more won’t matter because the value will be in working on it & driving it. You already know you'll be upside down on this immediately unless it’s just a parts car.
I see adding a sunroof that actually works & doesn’t leak as not detracting from value or maybe adding value.
I wouldn’t worry about keeping it OEM because someone wanting one will find a nicer original one.
It might be quicker to find a decent slant six car & transfer the four speed & fold down seat.