What the recommended steps for a break- in after a top end rebuild ? Oil, valves, etc
Replaced heads with new valves, springs, valve guides; new 96 mm pistons, and cylinders.
500 miles ?

Probably most important for a top end rebuild would be to seat the new rings. Take it up to redline under load and then decelerate to idle. Do this 4-5 times and your rings will be seated. Change the oil... Drive as normal.

I dont go past 3/4 throttle and 3/4 max rpm and constantly vary the load, and let off in gear a bunch to help seat the rings, i change the oil at 100 miles then again at 500
after about 1000 miles i start to drive it normally. It will be tight and run warmer the first 1500 miles or so ive noticed.

Thanks. Just what I was looking for. Sounds like the rings can be set at home; I'm thinking of a drive up the coast to San Simeon and back for the rest of the break-in; then change the oil again....

It's interesting to see different takes. Some were taught to take it easy during break in. Some are taught to hammer it. Hard to figure. Who knows which is right?

Don't over rev and lug the engine keep it on the boil all the time ,you need to keep gas pressure on the top rings @ all times,don't listen when people say drive it like you stole it that's BS.
My favourite running in place is a hilly area nearby where I live,keeps the engine working,I won't get into a when to change the oil debate but I do it fairly early in the running it process...sometimes I have been surprised @ the crap I have seen in it after draining.
Good luck .

Interesting: i can do a series of short drives of 60 miles mostly flat but a couple of hills ( 405 then down the 73 and return

And / or a drive up Hwy 1 to San Simeon, about 190 miles, overnight stay then return to Huntington Beach

I better load up on motor oil; looks like I can expect 2 changes ?

Most of the comments so far are directionally correct; however, I suggest you consider some points during the break-in.

First, driving the car with a light throttle (i.e. "babying" the engine), is not a recommendation that will be made by any engine builder I've known. Drive the car with light throttle will promote cylinder glazing which prevents the rings from every seating in.

The correct way to break in a Porsche engine is to drive the car "like you stole it", which means driving it hard. The caveat is that during break in, do not rev the engine past 5000 rpm. Also, you should initiate 6 to 12 instances at the beginning of the break-n cycle where you "bog" down the engine. To do this, take the car up to about 30 mph, put the tranny into 3rd or 4th gears, and then take your foot off the throttle allowing the car's speed to bleed down. As the speed gets low enough to stall the car, give the engine full throttle just before stalling and take the engine up to about 3000 rpm. Then repeat the same cycle. Applying full throttle to an engine that is beginning to bog down produces high cylinder pressures which serves to exert high outward forces on the piston rings promoting rapid seating of the rings.

Driving the car like you stole it means doing rapid acceleration of the car as much as possible during the break-in period while observing an engine speed limit of 5000 rpm.

During the break-in period, run a proper break-in oil such as Brad Penn 30wt Break-in oil. High zinc levels in break-in oils assure that the contact surfaces between tappets and cam lobes are properly protected during the break in period. Once the break-in period is completed, change to a 20W50 oil that has high levels of zinc (greater than 1300 ppm zinc).