I'm hoping for some advice. I just put a new cam and rod and main bearings in my son's 302. The problem is we can't get it started. I think the timing might be off but I can't figure it out. I have spark to the plugs and it's getting plenty of gas. I double checked the plug wires and they are correct. It turns over fine but it won't fire. I have the timing marks 6 degrees btdc. The rotor is pointing at #1. #1 piston is at the top. This might sound stupid but what is the dwell and could this have something to do with it. Any advice would be greatly appreciated!!  

Well Eric, couple of things to start off with. Its easy to get timing 180 degrees out. Meaning its firing when number one cylinder is at tdc on the exhaust stroke rather then compression stroke. You can pull out the distributor and turn the motor over ONCE till its at tdc again and then replace the distributor,,,or ,,, you can move the plug wires around until your firing at #6 plug,,or you can just pull out the distributor and point it to number 6 plug your choice. Remember firing order is counterclockwise as you look down on it. The other thing is of course did you line up the timing marks correctly when you put in the new cam and chain.  

I did make sure that the marks on the cam and crank sprockets were lined up correctly. It is possible however that it is on the exhaust stroke. If I pull the #1 plug and check for compression would that tell me if it was the compression stroke.  

If you have it timed properly, double check your valve adjustment.  The first time I changed a cam, I followed the book's instructions to tighten the adjustment until I couldn't turn the pushrods with two fingers.  That was BS.  The valves were not closing after that.  I was just a kid.  A compression check would have revealed it.  This probably isn't your problem as the engine will spit and sputter like it MIGHT run.  Dwell is related to the points gap.  If you have spark, worry about that later.  

It has stud type rockers. I don't think they can be adjusted can they?  

Well not if they are the positive stop type.

Yes you can put your thumb over the hole and have someone rotate the engine and you can tell if its on the compression stroke.
Normally a 68 has adjustable hydraulic lifters with press in studs. If you have a later model head it might have the positive stop(non adjustable type) rocker and stud. Lifters need to have been soaked in oil before you installed them if they were new. Otherwise it takes awhile for them to pump up. Low speed cranking is not good for a new cam and lifters, hope you slathered on the cam lube and used an oil with zinc in it.  

The dwell is adjusted by setting the points gap to a specified distance at maximum opening. A narrower gap gives more dwell and a wider gap gives less. Taking it to extremes, excessive dwell means that the points close too soon after opening, cutting off the magnetic field collapse before it delivers all its energy. Too little dwell gives the magnetic flux insufficient time to build up to the maximum.

Both conditions give a weak spark which gets even weaker as the engine RPM rises and produces misfiring at normal operating speeds. The dwell, as well as spark plug gap, do have an effect on ignition timing. The later the points open, the later the spark comes and retards the timing. The earlier the points open the sooner the spark comes and advances the timing. That is why timing is the last thing to be set in a tune-up.  

I'm not sure that your dwell questionwas answered completely. V8 dwell is set to 26 to 32 deg.

Like mech guy, I've seen dist. put in 180 off lots of times. Pull #1 plug and with the coil wire out of the coil(for safety) crank the engine until your thumb is blown off the #1 hole. Reset the pulley to TDC and pull the cap off on the dist (mark where #1 wire goes on the base of the dist first)  if you're close with the rotor to #1, set the dist body to coincide with #1 plug just ahead of where the rotor is. I also suggest you use staring fluid to get a very quick light off of the fuel mixture. ( if its close it should start.
The comment about too tight of lifters is also a good tip and may need further attention if the timing is OK. There are 2 different firing orders for SB Fords make sure you've got the correct cam and firing order also.  

Right, jlg, sorry.  The dwell is set to 26 to 32 with a meter by fine tuning the points adjustment!  

Just wanted to thank all you guys for your help. I pulled the distributor and turned the motor one revolution and put it back. It fired right up and runs awesome. I did put cam engine rebuild lube with moly on the new cam and lifters when I put them in. Also one the rod and main bearings. I also put a can of the Comp oil additive from the machine shop in the oil and ran the car for 30 minutes at about 1500 rpm for cam and lifter break in. Just a little fine tuning and it's good to go. I have one happy 16 year old son!!  Thanks again and I know who to ask if I need more help!!  

Gawd I love it when a plan comes together. good for you Eric