Dude I'm not an air head nor do I know it all, and you said yourself your new to skylines, so I can say without a doubt I know more than you about the subject and therefore I know it ugly,
A conversion is gonna cost you somewhere around 2500-3000 depending on what you get the gearbox for, and who you have do the work,
Therefore you just spent over $10000 on a skyline that looks like shit,
$7500 for an auto is not a good deal more so with that front bar