machining a head with some kind of resevoir, so as to heat oil...so one can, say, pump it through the handlebars or something for those dark winter nights, then yeah, worth thinking about...
technical complexities of liquid cooling prevents its widespread application...else youd be seeing every chainsaw n brushcutter with a radiator
buuuuut, if youre determined to be different...
knock out the central fins until theres only the top n bottom, bend up some 3mm ali sheet, to a close fit, get someone to weld it together for you, along with the fittings...in n out, top n bottom...
use the heater cores from a car...or two...
theres electric waterpumps to be had... not entirely necessary depending on radiator size and cylinder design. in fact, on small engines, any engines, too much water flow can be more detrimental than not enough!
on an r/c boat, for instance, while you can squirt water through fast enough to leave the head lukewarm or colder, its best to throttle it back til its coming out just under boiling point for maximum performance/longevity... oil gets thick when cold. metal likes to sieze when cold, etc etc etc...
the auto pressurised systems allow you to run the engine over 100 deg c without your coolant boiling. higher pressure, higher boiling point. higher engine temp = more efficiency
or even use some kind of retro worked fuel pump that works on case pulses? plenty of options really... you dont need masses of flow.
*suits mechanically inclined*