1.6 or 1.7 roller rockers

usally the number is stampped in them to lety you know if they are 1.6's or 1.7's. for valve lash go to this link and follow instructions
http://www.compcams.com/Technical/Instructions/Files/250.pdf
i'm not sure about push rods but i believe they are factory length. as far as which rocker to buy i say a guy running 1.7's on his exhaust and 1.6's on his intake.

the only way to set valve lash with your combo is with shims under the rocker pedestal. gt-40s have pedestal mount rockers unless they have been machined for stud mount rockers. i doubt it. rockers are usually stamped with the ratio. to adjust pedestal rockers..... bring said cyllinder to tdc compression stroke. bolt down rocker. check how much movement the lifter is preloaded. if it bottoms out or is very low, you need to add a shim to raise the rocker. stock engine that hasnt been apart should bolt together and not look back. but check anyway. heads that have been milled is usually when you need to shim.

damn....sorry. re-read yor post. you have guide plates. piston to tdc compression stroke. adjust to zero lash and then 1/4 turn to preload the lifter. if your pushrods are worn where they ride in the guide plate, you need hardened pushrods. you need hardened pushrods anyway with guideplates. stock pushrod length should suffice.