I have a 598 with a solid roller 730 lift 260 lbs on the seat 680 lbs on the nose. What push rods should I run I have jessel rockers on it

That seems like a lot of spring pressure. The testing we did said you can't likely use use too much push rod. We are using 7/16" .165 wall - double tapered. Tapered was necessary to get them to fit with our heads and we only tapered enough to get them to fit. What heads, cam duration and rocker ratio are you running?

I'm using dart pro 1 with a 262 /274 duration cam with 1.7 ratio

3/8 .120

It sounds like your cam is a some more aggressive than ours. Is your lift gross or net after lash? Regardless, the 7/16" with heavy wall is probably all you can get to fit. This may also require some light grinding at some points on the head to get clearance. Are the heads installed yet? Trend Products will likely work with you on a couple of demo push rods until you can figure out exactly what you can get to fit.
Custom fitting pushrods is really a project for a good engine builder unless you have more skills and tools than I have.

If you have set the stands to the correct height, and the heads are installed and you have the lenghts figured out. Call Terry Manton, Manton Pushrods. He will ask you about RPM, offshore boat, N/A or supercharged. I can tell you that a tapered push rod is not as strong as a straight. You may have to clearance for the pushrods,so be prepaired. You may want to call RM Builder,on your spring selection for the cam, with out the cam specs. I don't want to say; the pressure is to high. With 730 lift usually 230# seat 600 # open.

It may depend on ramp speed but isn't a little more pressure better than not enough.

On the testing we did with our combination, the 3/8" .120 wall push rod was not enough. Call Trend Preformance (586 447 0400) and see what they recommend for your combination. I think they will tell you outside of a few $, bigger and stiffer is better...ask you wife

Without the taper I didn't have a problem that I know of, no rub marks on the pushrods from flexing into the block or heads. 7/16 would be better but if the motor is already assembeled clearencing could be a problem.

Yes the motor is all together I built it 2 years ago