Need a approx. value to sell brother's Parker

[Bryan Liedahl]

Hi this is my first post so if I run afoul of protocol let me know.

My brother asked me to sell his parker for him and though I love most things firearms related, I know when I need advice from someone else.

From info found mostly on this website I know this gun was made in 1879. I'm not sure what the M and U stand for and I guess the 6433 is an order number. The 3 and 8 are the barrels weight?

The butt plate is recent replacement made of wood. Is there anything unusual that may have a bearing on value?

I really am in the dark about value, I have been told $600 and also $1400. There are a couple of guys that want me to give them a price asap. Any help would be appreciated.