to run 1.7s, mustang guys just bolt em on to stock roller 5.0's, occasionally needing a shim underneath the pedestal to get the right preload which is .20 to .60. the general rule among stang guys is if you can torque the rocker to 25 ft lbs 1 to 1 1/2 turns after the rocker is finger tight, youre good, if not shim it with shims provided with the roller rockers. i run them with the stock explorer cam, they bolted on with the correct preload using no shims
with that said, i dont even know if youre using pedestal mount rockers vs stud mount rockers which have a stud and locknut, and adjust w/o shims
ive got 4000 miles w the roller rockers (used crane 1.7's with the ford p/n on them, stock on 93 cobras) and i havent had problems , no extra noises, and i cant say if they added to performance cause i changed the whole drivetrain at the time but i do have plenty of power, it pulls past 4500 but i dont really hang around there often...enough
btw STAY AWAY FROM THE CHEAP ROCKERS theres a few guys on corral.net that have had crappy new sets shatter, destroying the motor...
I ordered a set of push rod length checkers from Summit(I think Trick Flow brand). Basically a micrometer in the form of a push rod. You put it in place and adjust your valve lash then roll the engine and look at the rocker tip travel path on the valve tip. Adjust it till you get a perfect travel pattern on the valve tip and now you know exactly what length push rods to order. If you know what range push rod length you'll be in you can get with ordering just one(about $12-$15 each) I ordered a full set(I think it was about $40).
1.7 rockers are just a higher raitio so you will get more lift out of your cam. For example a .480" lift cam is only .480" lift with stock 1.6:1 ratio rockers, if you go with 1.7:1 rockers then you will have .510" lift.
if youre running an aftermarket cam with high lift (above .480) i d check the pushrod length like hes saying just cause that sounds like a real good idea in the long run with big lift cams building your motor. plus you have a 351, 9.5 in deck height so your pushrods are 1.3 in longer
in my case the 1.7s just make the explorer cam the size of a stock mustang 5.0 cam with less duration so im fine with stock springs etc.
greenmustanggt on this board and many others on stang boards suggest the crane 2031 cam with 1.7s, something to look at while researching