alright... here are my results so far:
'86 NQ50 spree head onto an '83 PA50-II
upon side by side comparison the spree's combustion chamber is clearly much shallower. the head bolts right on. i was suprised how much smaller it is overall compared to the pa50 head... a LOT less cooling fins. not sure if that might become an issue or not.
compression test results (i have a cheap gauge, it's good for comparison but i dont know how accurate the numbers really are):
spree head (with head gasket) 130psi
spree head (without gasket) 145psi
the main problem with installing this head on a hobbit is the decompression valve passageway in the jug. with the spree head, there is no material above this hole to seal the head gasket over it... therefore it creates an exhaust leak which seemed to adversely affect my performance, especially from a dead stop. the bike didnt seem much faster or slower out on the road which may also have to do with the exhaust leak. i didnt take it out on the road without the headgasket because i figured it would start leaking pretty quickly.
unfortunately my base gasket seperated on me a little so now i have a slight leak down there which may be affecting performance as well.
for now i put the stock head back on, i need to come up with a way to plug that hole in the jug and also pick up a new base gasket. i may end up having the stock head shaved rather than using the spree head, afterall. the reduction in cooling surface area doesnt seem like a good idea especially since i'll be increasing compression at the same time.