They are probably fine - but you'll ahve to convince the buyer of that. Get them pressure tested and have that handy for the buyer. It's common to have them crack, and no - it isn't fatal.
The EQs are very different from the RHS heads. The EQs are basically stock Magnum design, with stock Magnum ports, stock Magnum rocker gear, a thicker area where the visible cracks appear, and variable bolt patterns (order the type you want - stock Magnum or stock LA patterns).
The RHS heads are a performance head casting, based on the Magnums. The ports are different and better, and are cast with provisions for both rocker setups. You order what you need - LA-X heads are the LA intake pattern and LA shaft rocker system machined for use. The MA-X heads are the Magnum pedestal type rocker system and magnum intake pattern.
Both are limited as far as lift goes without using longer valves and the right rocker setup. The RHS castings are heavier by a bit because of the extra material cast into them.
I like the EQ heads with the LA intake pattern for 273 to 340 builds that are milder (under 350hp or so). The RHS heads are for larger engines with the need for more lung capacity: up to about 425hp. Beyond that, once any porting is needed or there's racing involved - IMO you've outgrown these two head designs as far as cost vs return.
