Pushrod Length?

I too purchased a set of the miller mid lift rockers, 7/16, 1.6. I installed them on a 5.0 roller with Winsor Senior heads. With .500 lift. The first thing I had to do was replace the 1.75 inch studs with longer 1.92 inorder to have enough threads to secure the locks. Actually I should have used the 2 inch, but didn't want to fork out over a hundred bucks for studs. I figured the midlift with no problem, however you can't remove the roller lifters with the heads installed and you can't check push rod length with them not installed and it is almost impossible to check valve midlift or any other method without using a solid lifter because, despite all, they will bleed off a little even while priming the motor. Even a test spring is going to give you an inaccurate reading when using hydraulic lifters.

So to do it correctly I would have to use two sets of new head gaskets at a hundred bucks a crack. That ain't going to happen unless maybe I made my living racing this motor.
I used my home made push rod checker and got it as close as I could. I compared it to the stock pushrod and came up with a guess a mate of +150. I searched Summit and found one that matched. I ordered the cheapest set I could find at $60. Why spend $260 for a set of pushrods that might not work.
Well, I lucked out, they seem to be the right length or close enough which is all any of them are. I won't know until I run the motor in and recheck them. If they are good to go, I'll order a better set.

Comp Cams advertises these lifters to fit a 289/302 with retro fit roller cam. That is how I found them. Read that again!!

Bottom line, no matter who's method you use, it's very difficult to fine the perfect pushrod outside of a laboratory using hydraulic lifters.
That's just my opinion or maybe I'm missing something in the mix.

It's all about trail and error, but maybe someone else has a similar setup and it would give them a starting point. Maybe that is what the original poster was actually looking for.
Comp Cams method may work for some, but I know others who would never use that method to set up a valve train.
I'll be the first to tell you I'm no expert.

Retyler- You made some valid points and some- not so much. The standard method for determining pushrod length with hydraulic lifters is to replace them with solid lifters and then add in the proper pre-load to the equation.I may be missing something as well. I don't know if the hydraulic roller lifters you mention have solid lifter counterparts. I would think they do, but I haven't messed with roller lifters yet. However, for every problem there is a solution, and it need not require a lot of money or a laboratory to solve it. If you cant use a replacement solid lifter, you ought to be able to make one with $1.00 worth of epoxy. As far as head gaskets go, a $100.00 head gasket ought to come with a compressed thickness specification, and I'd be willing to bet that there is a way to match that with MUCH cheaper gaskets. Finally, I thought the whole idea behind hydraulic lifters was that they compensated for minor variations in valvetrain geometry, so- close should be good enough.