a 347 just seems to much of a stroke to me. 331 would be more comfortable in the reliablity. The 392 is great and you won't notice the extra 126. When you get used to the hp all you need to do is throw some AFR heads on it and bam you got 70 more hp to play with! On the 347 you probably have maxed out the hp already. you can't make it any bigger. The 392 you could punch out to 418 and still be safe.
just my .02
Sid
PS here is something you may want to look at.
http://www.dssracing.com/customercars.html
Sid