Well, I hate to foist my opinions on others, so I'll stick to the "tech" approach:
The Jardine will produce less HP and torque than the stock pipes. That's physics: the 4-1 pipe collectors need to be longer than the 500's frame to increase the header suction enough to make more power than the stockers did. The stock pipes on the 500 probably had more engineering in them than anything Honda did prior in that area, because they had to be short and had to try to produce more torque in the 5000 RPM range than they finally did: they tried to offset the short-pipe loss of midrange by increasing the intake runners, which did help some. The Yosh megaphones that finally removed that famous "flat spot" ended 8 inches past the rear wheel...that's what it takes, in terms of the pipe lengths...
The electronic ignitions: the Dyna 'S' will make less spark than the points. Mine will make more spark than the points, while still using them (that's in a nutshell: others have seen my novels explaining this elsewhere...
).
Tires: try to stay with the right size. They often get oversized on these bikes, which seriously reduces acceleration with two aboard. Stock front was 3.25, rear was 3.75 when new. A metric front today would be a 90/90 and the rear would be a 100 (3.50 equivalent), or possibly a 110 (3.93): I usually rin the 110 on a 750, which came stock with 4.00 rears. Metric tires let you run higher tire pressures, which also improves performance.
Avoid O-ring chains if you're looking for power: they lose almost 7% while a non-O-ring chain like the Diamond Powersport loses only about 3%.
Check the Thoughts Of Hondaman, where Steve captured some of my old 500 notes. One of the most significant things you can do to these engines is to port the heads. I have seen as much as 5 HP appear out of nowhere on them after a good port job and a K&N airfilter, using stock pipes. All we changed besides that was the mainjets, going up 2.5 size (I think that took mine to 97.5,back in 1973, but don't remember the exact mainjet number, at the moment).
The stock gearing was actually pretty good, unless you were going racing. Then we went bigger on the back by 2 or 4 teeth - but those engines often had cams to take advantage of the willingness to rev that those great Fours have. In those engines, we had to recurve the spark advancers to meet the higher RPM, too. That's a whole post by itself, though...
I think the 500 was one of the most beautifully styled bikes Honda ever produced...
