exactly what chimp said...
if you get the CA, dont' expect to be able to find parts easily for it, and the RB is a skyline motor... and an much older one... don't expect to find parts for it either without waiting a while... the SR is actually in america in it's FF form, so many of the parts are switchable.
Everyone agrees/agreed that teh CA was a great motor, it just wouldn't be very realistic to have in the states, unless it was a race-only car. The RB would require even more work... either way, to have one of these engines in a daily driver would definitely not be the best idea, but as a 2nd car would make a good project.
Where's CA18guy? he's all about the CA <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt='
'> I wanna hear his input