Ok, cam, Schneider Cams in San Diego is still in business and you get to call, talk to the boss (Jerry), tell him what you want and what you have, and he will grind you a cam. Clifford Performance (expensive), Isky and Howards all can get you a cam. There are other alternatives also. In fact, there are a handful of small cam grinders that can grind you a cam. I used Schneider for my last four cams and like the product and the fact that he will make up a grind to fit your needs.
Solid lifters for a 56 block, do not use the milk bottle style early lifters. They are for early 55 and prior motors, and some of the NOS milk bottle lifters are for a steel cam and not compatible with a cast cam. They will not work in the late 55 -62 blocks. You want to use the solid lifters from a 56-62 261 chevy truck motor. Same shape and design as the hydraulic lifters you currently have. You will also see solid lifters advertised for 55-62, same thing. NOS, RNOS or new manufacture, all good to use no problem. When I get home tonight I will try to post a photo of the two styles so you can see what we are talking about.
Push rods, don't mess around here. The after market push rods are tube style and way stronger then the stock push rods, and they are not all that expensive. A broken or bent push rod on the other hand runs the risk of doing a little damage. Order push rods for 56-62 235 chevy or 56-62 261 chevy, they are all the same length and style.
Hydraulic lifters, yes an issue. The new versions have a nasty little habit and reputation of collapsing within a short period. If you want a hydraulic cam and lifter, get real GM NOS lifters, or aftermarket lifters (Johnson, TRW, Sealed Power, Elgin) that are at least 25 years old and made in usa. There are two types of GM NOS Hydraulic lifters, 55-58, 59-62. Truth be told, I have never investigated the difference, I have always just used the correct lifter for the year of the block.
3X1, looks cool, tough sometimes to get sorted out for the street, especially if you are trying to run three Rochesters. I ran that set up for a time, still have the intake, could never get it to run great on the street unless I was buzzing the motor a bit. Consider a 2X1 with adapters (Langdon sells them) and run either a pair of 1974 Ford Pinto Holley/Weber progressive two bbls or a pair of the Carter/Webers that Tom Langdon sells. They will run way better on the street then two single bbl carbs or three single bbl carbs. If three carbs is what you are after, and you have room, then you should also consider three ford pinto carbs or the carter weber carbs. Again, progressive 2 bbls, like a quadrajet, small primary, larger secondary.
Fentons, they will work just fine. Clifford still sells real tube headers. Do a YouTube search for clifford performance and there is a video of Larry from clifford starting up a 235 with his headers. I have run old style Clifford long tube headers since 1981. Love them and love how they sound. There are some cheap sort of tube style headers floating around. Take a pass, they just plain suck. If running an offy manifold, they will generally bolt up to a stock exhaust manifold. So you could also cut a stock manifold up and make your own split manifold with the added benefit of keeping the heat riser system.
Speaking of offy intakes, if you flip one upside down, you will see two or three steel plugs staked into place. If you are going to run Fentons or Clifford headers, and you are not going to run the copper tubes for exhaust heat, but run hot water to the bottom of the intake (Langdon recommended and yep, it works really well), you have to weld little aluminum discs over the plugs. Those casting core plugs will leak if you dont.
