Sure, take your car mix in $15 - 25k and 300 is doable, don't know how streetable it might be. I Think that that the current crop of PCA GT3 911s might be in that ballpark
The list of necessary mods will be quite extensive and include but not be limited to
twin plugs
individual cylinder throttle bodies(or carbs)
engine management(delete if using carbs)
cams
valves
head work
p/c
rod bolts
lots of TLC