Without installing relays or having to rewire anything what is the best and brightest headlights/seal-beams to use in a 75 El Camino?

Mike

Sylvania Silverstar.

Available at your local auto parts store. When I bought a pair for my Elco, they cost about three times more than a regular headlight, but the money spent was well worth it. Plug and play, no wiring to screw with.

Are these a seal-beam type or do I need to buy the light/holder and then the bulb to go inside the light? Thanks

Do yourself a favor and use H4 bulbs in a conversion with a relay. Even installing a relay with your stock sealed beams will be an improvement. It is not hard to do.

Did you use a separate relay for both low and high beams?

Yes, you will need two relays. Low beam and high beam are two seperate circuits. Go to the 'sticky' at the top of the electrical forum and read the explanation of how a relay works, it is well written.
Just throwing larger or brighter bulbs into your system will not give you much light increase unless you have the wiring size to carry the load the brighter bulbs will draw.
You could potentially damage the stock wiring if you increase the load too much.

Are these a seal-beam type or do I need to buy the light/holder and then the bulb to go inside the light? Thanks
Yes, they are a sealed-beam type. It is a direct replacement for your original headlights.