First of all I have a set of unused speed pro ht817 lifters. I installed a isky mega 274 cam. Do I need better lifters than these? I saw that speed pro also has a ht817R which is for high rpm. Second what size and type of pushrods and rockers do I need? Its for a 383 with Dart heads.

I think they will be fine. As you stated, the "R" lifters are for higher rpm. I don't think you need them for that cam.

Stock diameter rods will work fine. You should measure for length. Depending on spring diameter, stock type long slot rockers are fine. However, they often will not work with larger diameter springs. So that is something you'll need to check during mockup.

Pat, this is my spring set up. How do I measure for push rods?

Elgin 21-4N stainless steel valves with undercut stems for high flow
Pioneer Z28 style 1.250" OD single valve springs with damper
Spring Specs: 110#@1.700 90#@1.750 325#@1.200 Coil bind @1.150

With 1.25" springs stock type rockers will work. Do a search in this forum, pushrod length has been discussed several times. If you can't find want you need, post back and I'll go through it.