Chris, I was thinkin a 70 chevelle would have front disc brakes, but in checking I see that it could have either, But a cheaper alternative would be to replace the front spindles and drum brake setuo with the spindles,rotors from any 1970 to mid 80's midsize G.M. such as chevelle,mont carlo,malibu,skylark,cutlass etc. these should be available from a salvadge yard,at a reasonable cost, you'll need a new or rebuilt disc brake master cyl. & proportioning valve ( I would get the valve from the salvadge yard also) be sure and purchase new brake hoses & new or rebuilt brake calipers, if your looking for rear disc brakes your just about stuck with a kit or peicing things together wich can get complicated,
As far as the suspension, the Chevelle had a very nice setup and I see no need to change it, other than a thicker sway bar in front and adding a rear sway bar if it doesn't have one already, I would replace all the ball joints,bushings"front & rear",,steering linkage etc. with nothing but MOOG items, Put 4 new Monroe Sensatrac shocks, and have it Aligned by a pro and ya should have a very nice handeling and stopping Chevelle, One thing I didn't cover where the springs if ya feel the need to replace em stay with the application as I've seen lotsa guys put the big block springs under a chevelle and it gives it to hard of a ride plus it looks goofy cuzz it makes the car sit up too high.....