[steve25]

If you do a hot cranking compression test and all the cylinders are with in 15% then I would at least initially conclude that the rings are sealing ok.

Next up when the exh smoke is Blue is the condition of the valve seals , especially if the blue smoke does not start right off the bat, but until the motor starts to get warm!

1) The seals could have dried up,

2) they could have been installed wrong.

3) they may have busted from being hit by the valve spring retainer due to inadequate clearance, but if the motor uses only a stock Cam of .406 this should not be the case!

4) or like when your same issue was seen from brand new aftermarket heads of a friend of mine that had been assembled with seals for 3/8” stem valves and not the 11/32” stem valves that where used in the heads.
This issue took us quite a while to figure out as we progressed down the list of process of elimination!

Also a true 100% stock rebuild would still be using the stock valve spring retainers and the stock valves which have a second groove below the keeper groove to hold a O ring seal which the stock retainer is designed to hold.

It may be that the heads where not assembled with these seals , or like I posted they have dried up over time and just cracked into fragments.

You need to look to see if during the rebuild the heads had the tops of the valve guides cut for what’s called positive type seals which could seen thru the valves springs, or if like I posted they are still set up fully stock and use just a Valve stem O ring under the keepers.