Welcome to the Team Jim!
Passenger blocks are weaker than truck blocks (which is about all that have survived up until today), but the truck block has a cut out in the block that drops static compression which can be made up for with a higher compression piston. What can not be made up for is the lack of squish (forced turbulence in the combustion chamber that promotes fuel and air being throughly mixed prior to ignition).
Old style valve covers used to cost over a thousand dollars, but Edelbrock makes new ones now from the same molds as the old ones, only for a lot less. They will throw in a set of better breathing heads with bigger valves made of aluminum for a few dollars more (painted Chevy orange they all look alike).
Don't like the selection of blocks available? World Products is casting new 409 blocks with four bolt mains that accepts a modern BBC crank so a 481 cubic inch motor (or bigger) could be in your future. You can put a BBC crank in a stock Chevy 409 block but you have to turn it down (thus weakening the crank) which is why there are so few 409 blocks around today. The World Products block uses the same tough high nickel content nodular iron that Chevy used in its truck blocks, so they are stronger than a stock Chevy block as well.
Modern carburation has removed the need for dual Carter AFB's sitting on an intake manifold. But if you want the headache, they are reproducing better breathing dual quad aluminum manifolds (that look stock painted orange) and topping them with the newer AVS style Carter carbs; only now they say Edelbrock on them.
Cam technology has improved mostly due to improved metallurgy in the valve springs. A new HEI distributor is way better than a dual point distributor, and modern capacitive discharge ignition boxes remove the voltage drop off above 4200 RPM that HEI suffers from.
Even oil has changed since the old days. Modern motor oil lacks the Zinc and Molybdenum that a flat tappet cam requires, and your rings and other metal parts that rub want, to survive as well. So you HAVE TO use a roller cam with modern engine oils. But that is a good thing because technology (self oiling roller bodies) and metallurgy have produced fly weight solid rollers that have little to no valve lash for quiet maintenance free operation.
Spark plug wires now are made with spiral core technology so you can listen to a transistorized AM-FM-XM radio without static or frying any other electrical devices such as automotive computers to control stuff like transmissions or EFI or even a digital quartz electric clock.
Any other questions ask away.