I am replacing my timing gears and chains on a 1976 4x4 f150 390. I turn engine over until the timing marks line up, pulled old gears and chain off and kept in original position and laid on work bench. When I went to put new gears and chain on I noticed the old cam gear had from bottom to top -timing mark, pin hole, then bolt hole. And it would not go on. The new cam gear had from bottom to top - timing mark, bolt hole, them pin hole. This is a Edelbrock timing set -7808. I bought from Advance Auto and checked the part numbers myself, and box states for 353-428 . I then checked the dizzy and the rotor was facing opposite #1 plug wire. If I rotate engine until rotor faces #1 plug wire then the timing gear will go on, because it rotates the pin down. Because it is the weekend I could not contact Edelbrock to check the the parts number. My question is if the timing was off 180 degrees wouldn't this have made the truck run raged? The engine was rebuilt about 10 years ago and changed from a 360 to a 390. I don't know it they just didn't worry about it being set right or not.
And should I correct this and if I do will I have to change the dizzy?

 

Put the new gear (and chain) on with timing mark at the top. Then rotate engine 1 turn. Marks should now line up. If not, you may be off by one tooth and need to fix that.

It appears that sometimes timing gear manufacturers sometimes put the timing mark 180 out from the OEM stuff. It doesn't hurt anything, but the marks will align on an alternate stroke... i.e. the exhaust stroke vs the power stroke, or something like that.

You could also rotate the cam 1/2 turn and then the marks would line up, but the valves and pistons might hit during the process, so I'd just install with the mark up, and then rotate the whole thing to make sure the marks line up on the next 1/2 cycle (1 turn of crank).

 

When your done setting up your timing marks and install the chain, pull the plugs and rotate the engine two revs. by hand just to be safe.

 

And if it hangs up - do not force it