converting my parkson 1na

hi there im currently in the process of converting my parkson 1na, now my mill has no quill so my first option was to try and lift the knee as the Z axis but as you can imagine that is very heavy! the spindle (int40) speed has 1250 rpm as its max so im debating about building a seperate head with its own spindle on that can produce higher rpm and this is wherre your advice comes into play!! do i
A; buy a seperate spindle, either er25,32,bt40 and use pulley and belts??
B; buy 1 of those air cooled spindles that has a motor built in and run with a vfd??Attachment 31094 Attachment 31093 Attachment 31095