"Ruger MKII all weather 300 win mag"
Good!
"great condition with a hogue overmold full bedded stock"
Bad.
Most people don't like these stocks. Many 'All-Weather' buyers are specifically after the "boat paddle" stocks. As such, the Hogue will usually subtract from base value.
"fully floated barrel"
Indifferent. It's a Ruger. Their barrels are too unpredictable. The average buyer will not care.
"warne maxim rings, Redfield Revolution 4x12"
Scopes are considered bonuses by 99% of buyers. Never include a scope unless the buyer is specifically paying for it. Rings fall into that category as well - except with Rugers, since Ruger rings are special and a factory accessory that shipped with every rifle. With Rugers, the rings are expected to be there. Absence of such subtracts from the rifle's value. Warne Maxima rings are not helping here. Most people do not like split rings.
The rings are a net-negative, with the scope possibly pushing things to a draw.
"and has a professional trigger job done."
Buyer's preference. Some might pay a couple bucks more. Most don't care.
I'd be at $450 or less on it, if it's in truly great condition. ...With one caveat: Year made matters to some buyers (like me).
If it was made between '91 and '93, I'm dropping value by $150, in order to create a safety buffer for possible barrel replacement. For '94/'95, I might still knock $75+ off it.
If your friend has seen it shoot, and is satisfied, then none of the year/barrel stuff matters. But, to me it would. '91 and '92 used both crappy contract barrels (mostly Wilson) and Ruger's new in-house hammer-forged barrels (but they were still learning the process and machinery, and fine-tuning the equipment). '93 was all hammer-forged, but quality was still sub-par. Things didn't really level out until about '96.
In this case: Add ~$75-100 for the scope, if it is specifically part of the deal.