i would go with the 302. i'm putting a 351 in mine, and they both fit...but you have to do a few minor mods. especially the oil filter. it sits right where the steering shaft is, you have to get a relocator. not too expensive. another thing is the oil pan might have to be converted to a dual sump.
this site gives some nice info on the swap. i'm not using heat or ac, so i have no answers for you, but this site does.
302 will have a little better clearance though, due to the smaller deck height. hopefully that helps