1) Valve springs, I don't find much information about them. I go on Comp's site and it doesn't seem to spell out specific hydraulic roller springs.
If I am going to use a hydraulic roller, I want all the valve spring I can get. They used to tell you what spring goes with what cam, and I don't want to reuse the old ones.
Can I use my shorter Mopar Performance dual springs, that I have always used on 340s?Comp recommends springs for every cam they make. They are in the catalog, and the spring section of the catalog lists all the pertinent specs. All hydraulic rollers spec either dual spring assemblies for them or the conical springs. Both need machine work to fit. Your machinist should be doing that work as there will need to be cutting on the guides to get the seats ready for dual springs, and the guides need to be cut for the small seals that are required. You can raise the spring installed height in severa ways: cutting the spring seats, using longer intake valves, or using special retainers that will raise the spring hieght. You machinist will know how to do that.
2) push rods, the stock ones are tooth picks. But due to the nature of the roller lifter, will a thicker pushrod run into interference with the large hole in the 308 head? You will need to either buy the best 5/16 pushrods you can get (and measure for proper length first) or clearance the "top and bottom" of the pushrod holes in the heads to run larger ones.
3) Rotators, why would I want to keep them? Makes me think I am working on a SBC. The exhaust spring is shorter due to them. You do not run these on any performance engine and you'll have to buy new retainers for whatever springs you end up using anyway.
4) should I retain those huge/agressive stem seals? They are smaller physically, and they are a positive seal rather than the large umbrellas. They are mandatory for double or conical springs. Not really "more aggressive" but they work better...
5) Should I just drop the hydraulic roller and put a conventional cam in it? That's entirely up to you but I feel there is a lot more concern over failed camshafts then a real problem with them. If you want a roller, spend the bucks and do it right and runa solid roller. If you don't have the bucks, learn what must be done to keep the aggressive flat tappet cams alive and do it, or chose a milder flat tappet cam and don't worry so much. Again, working with your engine builder/machinist will go a long way to helping you understand the choices.