Take the head off and give it a quick clean, turn it upside down so it's head gasket side up and pour a little petrol in the combustion camber. If the valves or seats are worn the petrol will seep through to the inlet/out ports. If there is only minor pitting just use course then fine grinding paste and a valve stick. If you've taken the head off then I personally would replace the tappets and valve seals while I'm at it.

At this early stage and without cooling the only thing you can do is take off the rocker cover and rotate the engine by hand and see if the lifter is slow returning after being compressed.
A compression test will show if your valves arnt sealing
Hydraulic lifters are renowned for building pressure slowly after sitting for a long time

if the lifters were not full the valves would be less open.

it may just be a sticky valve.

TT

If the lifters are slow returning then valves would not close

They don't return.

They fill with oil and expand to fill the gap between the rocker and cam and move in the follower bore. Once full they stay full unless faulty.

TT

They have a spring in them and the fluid volume changes as the cam rotates

Why on earth would they do that, and how?

You need a constant distance between the cam and the rocker otherwise your valve timing and duration would be all over the place.

TT

I'd still say it needs running up to proper temperature for a while, and possibly and oil change if not done already.

Some reference material from a well known publisher, :D

http://www.angelfire.com/bug/joro/manualz/1737-02B.PDF

Got the official ford "Technicians Product Information and Training" here.

TT

I got Tis, it was just easier to find something online than find where I stored the ISO lol