kdavies3 Kev Couple of things
Do you have the correct length of the pushrods?
End stands are a MUST for any motor with shafts, I have 2 shaft broken over
time. 1 was standard shaft and the other was heavy duty. Also make sure the all the surfaces are flat. Thiner stud goes in the oiling hole to rockers. Run an .080" oriface in each head. This will help help more
oil in the bottom end.
Lifters if you filled them and they will not bleed down, Pull them apart and drain most the
oil. Just remove the clip on top. Clean out
oil and reinstall with a dowel stick.
You need to get the correct pushrod length to keep the rocker end in the center of the valve top trough the whole open to close event.
Adjusting valves, Adjust to contact of lifter and bottom of rocker and 90 degree turn and lock off adjustment. Reason for this is if you miss a shift or high rev the motor there is less chance of mr. valve kissing mr. piston and doing damage to motor. This is a cold adjustment.
I hope you are running a HV oil pump with an 80# spring in it. FE motors need and love oil. 7 quart oil pan also and over fill it 1 quart. FE motors have slow returns from the heads. You should be able to goggle how to check pushrod lengths and setup. Good luck. Ps IMO not a good idea to try and collapse a lifter full of oil. easyier to remove the clip but be careful and have a good grip on it. IF you have the intake manifold on depending on switch one you can sneak the lifters out of their bores with a mini magnet and get them out through a hole between head and manifold. If no hole, you are pulling the manifold. Also make sure none of the pushrods are hitting the holes in the manifold. May have to grind a little for clearance. Rick L.