Installing a cam is a biggish job if you have never done it before. You would be best to buy a "How to" book on Mopar LA engines and read up on it first. You would be best advised to get new springs. Single with damper (not double springs) will be fine, Comp will recommend the correct ones on their site. The would be in the vicinity of 115 pounds seat and 285 pounds open @ installed height of approx 1.7". I also bought an Extreme Energy but mine is a Hi Lift (0.525) If the lift is only 0.507 on yours i don't think you will need to touch the guides. You can leave heads on but the inlet man. should be removed and a new double row TC fitted, if not already done on the rebuild previously. the 69 340 should have a DR TC anyway from factory so they should have replaced it with one. However if you leave the heads on you will have to get a tool to swap the valve springs over with the heads still on, there are several types available and will save a lot of stuffing around by not pulling the heads off. You will not need to touch the cam bearings. If it was rebuilt properly they would have checked/ and /or replaced these, if it was acid dipped (chem cleaned). Cam bearings do not usually wear that much anyway unless the engine has had a lot of bad stuff in the oil or had an oiling supply problem. Once set up with the timing chain marks in the correct position it is always a good idea to setup one inlet and one exhaust and check your clearances. But that is not a very high lift cam so you should be ok. Hope all this has helped.
