904 dilema HELP!!

OK...here is the deal... bought a 66 & restored it to BOND with the girlfriends 19 yr old son....he spent 4 days working on it and joined the ARMY...on one hand he is an idiot ( joining during a war is noble but stupid) on the other I am kinda proud of him...he was kinda wimpy and that was a bold move...ANYWAY...
I found a 69 340 big valve J heads and had it reworked...it came with a 904 no clue on the year and it was not attached....I went thru it for around $300 and made sure it was all where it was supposed to be.... AND I know the narrow 66 has issues with 727 fiting.....OK so now we are getting ready to bolt it all together.....I read an article that says 904 have a 6 model & an 8 model....hruumph how do ya know? I also read if you have up to 325 horses 904 will take it just peachy....1 HP past 325 and it will pretty much blow up!! LOVELY....not that I mind switching tranny's but I have heard the tunnel needs to be modified ( cut away and enlarged for a 727) and the underside and inside have been blasted & painted...seems a waste to do that all over....

SO here is the questions.... are all 904's the same? if not how can you tell the difference? any way to get one built that will handle the 69 340 HP? what is the approx cost for such a venture?..... The kid ( was a motor head) and he is in IRAQ....for the next 5 years!! in the meantime I have a lump of parts that need to become a car.... suggestions on transmissions and associated modifications & costs WELCOMED!!