Lets see if I can make this sound sensible.

I had a 360/727 combo built for my 57 Plymouth. Everything is/was out of the box new and now has about 1000 miles on it.

Cold cranking the engine, there has always been a lifter noise for the first 10 seconds then goes away.

Last weekend, the noise was constant for about 30 seconds and went away. I got out on the highway and noticed upon deceleration, a muffled lifter noise would show up. So I drove home about 2 miles and parked it.

Where do I go from here? I pulled the v/c and noticed one of the rockers had some rocking play where the others were solid. Bad lifter? Wiped cam?

I'm good with general external work. I have never gotten into an engine myself.

double check for a exhast leak very carefully

you can waste time/effort/$$ chasing a lifter ticking with a exhast leak,IMHO

the lifter tick at start up goes away as the oil hits it and pumps back up..

does the oil filter have a drain back valve in it??

are they adjustable rockers??

some will have some movement depending where on the cam lobes things stop at,some open,some closed,some closing,some just opening..ect..

was the engine run in and cam lifters broke in on start up of the new parts??

my guess would be an exhast leak first,then after that is ruled out,look else where for it

It is not an exhaust leak. Definately under the valve cover as it is running. The engine was broke in at initial start up, running different RPMs through several cycles.

As far as the filt having a drain back, I don't know. Does WIX drain back? BTW this is an LA360 with non adjustable rockers.

Hows your oil pressure? Do you have a mechanical gauge hooked up?

You might try another filter

then he should have bushed the lifter bores to correct it and the pushrod angle,IMHO