1974 Dodge Dart Swinger Hardtop engine swap

Yes any small block starter will work. Iirc even the slant six starter will work. I'd recommend a pre 99 ram or Dakota magnum starter. They are cheap readily available and work 100 times better than the original and there smaller and lighter!
As for the value the 340 is a good find it will add resale value to the car depending on the buyer it could also hurt. 74s are not all that sought after or collectable to the big money markets so I wouldn't worry about it id just do whatever makes you happy. I do think a 340 dart would sell for more than a slant 6 dart regardless of the year or originality. Just my opinion tho