new kid here

What did the 87 motor come out of? If it was out of a mustang it should have allready been a roller motor. And then you could just use the stock push rods.

^ Welcome!

Im pretty sure that you can use a stock push rod. But somebody will be in here before long that can help.

First you need a solid lifter or a set of checking springs. Sometimes you have to use the checking springs as the valve springs will bend the checker. Lets assume you are using checking springs installed on one intake and one exhaust valve. Make sure the lifter is full of oil and is the plunger is all the way up

Roll the motor around until the lifter is on the base-circle of the cam. Color the valve tip with a marker. Install the checking PR and the rocker. Adjust the PR so the roller tip is centered on the valve. Roll the motor over two revolutions and remove the rocker. Look at the pattern on the valve. You want the narrowest pattern possible. Centered is not as important as narrow. Keep trying different lengths until you get the best pattern. Measure the PR and add .020 (for the lifter preload).

Repeat for the other valve.

Now sometimes it is hard to get the pattern to show especially if you are using checking springs. I've use different methods but the one I feel is easiest is to use a LIGHT coat of black rtv on the valve stem. This will show the rocker sweep really well. Make sure you wipe all of the rtv off the rocker and the valve stem each time you check.

If you bought the good COMP checker then you just count the turns to get your measurement. I've also used that checker on some fairly stout springs with no issues so you may just need a to make a solid lifter. This is where it comes in handy to have a couple of old lifters laying around.