i have 74 challenger with a 360. i'm on a budget. i'd like to get 450-500hp. maybe do the heads 1st then in the future do the block. i'm thinking of getting edelbrock rpm heads. i heard its a direct swap. i have 650 edelbrock carb, w/torker 2 intake & headman headers. should i keep the torker 2 intake or maybe get edelbrock air gap intake? i'm thinking of getting the heads,cam,maybe intake. i think this set up is about 300- 400hp. what do u guys think?  

Edelbrock heads are great, however you will be bolting them on a low compression motor which is not a good thing. You will effectivley be lowering the compression further. How, the Eddy heads are aluminum and aluminum heads need at least a half to a full point more compression to work as effectivly as steel heads.
You could compensate by using thin head gaskets, but this is still not enough.
The proper way to do this would be to install a set of 10.5 compression pistons with the aluminum heads.
If you still just want to do the heads first, then consider a pair of steel heads from a 340/360. With port & Polish they will flow plenty close to the Eddys and when the rest of the work is done they will be a great basis for a 450+ HP small block.
 As far as the intake, the air-gap is probably the best intake for a street strip car and has excellent bottom end/mid-range and top end, were the torker is limited on the bottom end.
Cam? you didn't say if you wanted a hydraulic or solid.
Comp. cams has a nice .507 hydraulic, Mopar performance has a great solid, 284/.528 this is my favorite and it makes a ton of power.
If you go solid you will need an adjustable rocker set up, mopar performance also has a reasonable set from proform.  

which is cheaper, do the block 1st or heads? if i do the heads, r my 360 heads good on a 74?  

74 heads are very good and cheaper than doing the block first. If you do them right e.g. a pro machine shop, they will almost flow what the eldelbrock heads flow out of the box.
I had a set of 74 heads done, cut .040 off the face, to increase compression, installed thin head gaskets,   installed 2.02 valves & 1.60 stainless valves, ported/polished all for half the price of edelbrocks.
For the heads to work properly you will need headers, intake, 750 carb, cam & lifters.  

i have  headers(1 5/8). i'll get the eddybrock air gap intake, cam,& lifters. will my 650 carb do for now until i get the block done?  

Yes a 650 is good for a street car.