Wing wizard Williams will, of course, be among the first names on coach Warren Gatland's team-sheet, such are his mercurial game-breaking qualities.
A single try at Croke Park would haul 31-year-old Williams level with Gareth Thomas on 40 Test touchdowns for Wales, equalling a record it took Thomas 100 caps to compile.
Williams could also get there in a remarkable 45 fewer games, when a 40th try would also see him match the combined tallies of Wales greats Gareth Edwards and Gerald Davies.
That is not bad for someone whose initial rugby aspirations were just to play - and score tries - for his local club Amman United.
Williams said: "I seem to be getting better the older I get - and I hope that can continue for a while.
"I am relishing going out on the field and loving every minute of it. That's the most important thing, enjoying your sport.
"The day I go out on the field dreading playing or not wanting to play is the day I will hang (up) my boots, but at the moment I am as hungry as ever.
"I am a striker - I enjoy scoring the tries. That's my job, but I don't really set myself targets.
"I've had seasons when I've felt I haven't scored as many tries as I should have done, and I have worked on aspects of my game accordingly.
"As a wing, you should be scoring tries. That is what you are getting paid to do.
"The last couple of seasons, I've scored a number of tries due to the fact I am getting involved in games a lot more. I am a lot happier when I've got my hands on the ball."