Hi! where from austria are you from?
i also think the 650 DP will be fine if street only. But i´d suggest a bigger cam, check the XE275HL out....should work with the supplied springs (it seems you got these procomp heads from the moparshop? They say springs are ok for use up to .520" Lift - should work with the XE275HL and 1.5 Rockers), the XE274 is too small in my opinion. But if you already have it....use it.
Are you sure about the compression ratio with this pistons? i think with 65cc chambers and +5cc pistons compression is between 11 and 12....could be a problem with detonation (more with the smaller xe274 cam) and pump gas. Check it out!
Michael
