OK,  to clarify this for anyone following the post, using a washer, the washer goes between the cap and block NOT inside the cap between the cap and spring.

That's where I was confused.  With the washer, you're moving the cap away from the block.  Understood. Thanks Doug for the clarification.

Howard, thanks also for the tip.  If I was going to cut the spring and keep the ball, I think I'd cut from the side that would face the cap only so as not to score the ball.

 Thanks for all the help guys.  Hope to see some of you at MME.

Mike...I recently took the spring of my Sprite engine to a grinder to shorten it until I had the oil pressure that I was after. When doing this I made sure to go slow on the grinder in order to let the spring cool down every so often. I trimmed both ends and it didn't take much to reduce the OP.

If you're going to do this, trim just a small bit, install it and check the OP. If it's it's still high, give it another go. Do it in baby steps. I had mine out and in three times before reaching the desired result.

When you tighten the cap you are compressing the spring.  When you fit thicker or additional washers (big ones on the dome nut) you reduce the spring compression which means lower force on the plunger (or ball).  That means the relief valve opens at a lower oil pressure.  

Don't confuse this with adding small washers between the spring and dome nut.  Fitting washers between the dome nut and spring increases the spring compression which means higher force on the plunger.

There are different springs out there.  Some will have a higher spring rate, some are longer or shorter.  Just keep in mind your goal.  To reduce oil pressure, reduce the amount of compression on the spring.  

how does adding a spacer under the cap lower the pressure?  I would think that is increasing the pressure on the spring/plunger/ball.

My thought is the spring tension on the new spring is greater than the old spring that I had stretched. Even though one is longer, the new one I think is stiffer.

Adding a washer would increase the tension on the plunger/ball. Or am I missing something?
 
I"m not against adding a washer or two, just want to understand this science correctly.

Adding copper sump plug washers under the relief valve cap will reduce oil pressure.  If you fiddle with the basics (like replacing the plunger) you do need to make the other necessary adjustments.

Alex is correct, of course  oil pressure has nothing to do with seal leakage...

Cheers, Ian

Oil pressure is not the same as oil flow - yes, they are closely related, but you can have one without the other.  Think of a hosepipe with your thumb over the end, the tighter you squeeze the higher the pressure but lower flow as you restrict it.  
Oil pressure is a combination of many things, one of which is the pressure at which the relief valve lifts to dump excess flow into the sump.  It is also imperative to set the running oil pressure and disregard what it is at tickover.

Leaking tappets chests are symptomatic of gash seals not excess pressure.

If you spring leaks elsewhere, unless you've popped the gallery plugs out it is again down to poor seal prep not excess pressure as the oil galleries are effectively a sealed system between the pickup pipe and the journals.

Bear in mind that a ball bearing isn't always the best solution, I've reverted back to the factory relief plunger after problems with a ball, but once you've used a ball for some time the seat is incompatible with a normal relief valve due to reshaping/damage.

https://www.minimania.com/part/HPS4-CHROME/Adjustable-Oil-Pressure-Limit-Kit
yes 

I"m guessing the cut end goes to the cap.

When you put in a ball instead of the standard plunger you need to shorten the spring not stretch it.  Normally this is done when you switch from the plunger to the ball.  Say you had 60 psi with the plunger, car warmed up an at idle.  You would then switch to the ball cut say 1/4" off of the the spring.  You should have the same pressure you had with the plunger  (Adjust as needed).  An extra washer with the cap will lower the pressure, as will fitting an adjustable cap.  You can buy or make one.

This engine was built 25 years ago with a central oil pick up and competition oil pump.   I had initially stretched the stock pressure relief
spring and put a ball in there instead of the stock plunger.  My oil pressure was about 95 pounds cold. I've not run it long enough to see if it drops but the  cork valve cover gaskets was weeping oil.   I replaced the spring with the stock one, which is about 1/4" or less shorter.

Now the pressure is at 100 lbs.

Any thoughts as to how I can lower the oil pressure?

I think having the oil flow so fast might actually lessen the lube properties. Am I right?

Also , I"m pretty sure this high pressure will eventually cause more leaks in the engine.