CB400F fork set up is a direct swap without the fork ears/covers, but you can also run them without the fork ears/covers and with an aftermarket headlight bracket. personally, I like the fork ears myself... Switching to 550 forks will require a triple tree swap too -- fork tube diameters are 33 for 350F and 35mm for 550.
I'm a fan of the marving set ups simply because exhaust in German is "auspuff." I've run 400F exhausts on 350Fs, but it requires changing to 400F pegs, linkage and brake lever (but that also sets the pegs back about 6"s -- if you want rear sets with low bars it's a good way to do it). The bike in my photo has the stock air filter set up with 400F pipes, and didn't require rejetting. It also has run great for about 17 years like that.
I have also found that Kendas are good and reliable and inexpensive, but I'm not pushing them too far (but they'll take some tight corners...).