Dont do the 273 because of what everyone else says.
Stock there is no kind of power what so ever.
Even for a daily driver its not good, no torque at all.
Aldough i did manage to get my 273 heads with 1,9 int and 1,6 ex flow better than a set of x heads at 145cc. 228 cfm intake and 190 ex.
A 2.02 int valve wouls increase flow a little more but wont fit a 273.