69771-16 is the kit with a whole set of rockers. the part you linked is a single rocker arm (not sure if it's left or right offset or what)
as far as shafts, if yours are cherry you could use them.
pushrods - it varies like people have said. they sell cut-to-fit sets; you need a checking tool as well, which is just a pushrod you can adjust the lenght, and when you get it right you measure the lenght and then cut your pushrod to match.
basically you cut them and press the cup end onto the pushrod so the overall lenght from cup to ball is what you need.
if you go with 1.6 ratio i'm pretty sure you will need a custom lenght.
on my old 340 dart i used a set i got off a 273 from a trashed 66 barracuda in a junkyard. i grabbed the shafts rockers hold downs pushrods and was out the door for $25 bucks lol
fit my 340 just right, i had unmilled 2.02 heads with springs for my solid cam (.550) i had no clearance issues.
in an ideal world, if you go 1.6 you need to get custom pushrods, cut them to fit properly, check all alignments/clearances making sure the rockers dont hit spring etc rocker is centered on the valve stem, valves have plenty of clearance from the piston, etc etc.
and if you are going through all that trouble you should be running a solid lifter cam at that point, because hydraulic lifters will pump up at 6000 or so and then you start breakin stuff. soilds can go much higher rpms, i ran mine over 7k no problem.
