pull valve cover(s), identify faulty lifter (if that's all it is), remove rocker arm/shaft assembly, intake manifold and valley cover...pluck out the offending lifter, replace and reassemble.
Oh...ok! Sorry about that! Thought I read somewhere that they were all solid lifter. What ones would have been hydraulic...the later ones from the 60's or? I have one from a 67 Belvedere that I may run in my 63 Dodge.
This is on a 56 custom royal all original. Built many a engine for my dragster and cacklecar, I dont like leaning over a fender but if its not a big deal I will do it for pops.
The original problem was not saying what Poly he has. He's now said it's an Early Poly that is Hemi based, so..yes they have hyd lifters. Had it been a late "A" Poly the answer would have been...no they don't(except the one year only 326 Dodge).