i vote for the lucky mod! (drill through and bolt both sides, red loctite on the bolts)
if you have a drill press, half hour of your time and you just saved a bunch of money!

 

I do agree that if there is a difference it is very small, because many have swapped flywheels with no ~noticeable ill effects. I seem to recall reading that the 7.3's had more precise engine balancing, which may be the extent of the difference. Note the section from the service manual update that says 7.3's have cylinder bores and pistons stamped A,B,C,D that need to be matched, or replaced with an S stamped service piston that will work in any bore. This indicates to me that the 7.3's had different tolerances than the 6.9's. It may be splitting hairs over the flywheel thing, but given the choice I (personally) would avoid running the "wrong" flywheel ... Just in case! LOL.

 

I'm sure I'll catch a lot of flack for this opinion, but hey, after the flywheel balance debate I seem to be on a roll! Anyway, my advice/opinion would be to stay away from remanufactured engine and transmission. I simply don't trust the quality of the cores they rebuild, and you won't know what you have inside in terms of oversized parts, how much metal was machined off the heads if any... and on and on. If the engine being rebuilt experienced a violent failure, extensive machining may have been required which could compromise its viability for further rebuilding in the future. I also don't care for the idea of an engine that was build from a bin of parts instead of rebuilding an original unit. You may or may not get a late model 6.9 block with stronger casting around the block heater etc. , there was a member here who went through multiple reman 7.3's under warrantee because they were sleeved, and the sleeves were dropping. Not likely that a 6.9 would be sleeved, but not impossible that one bad cylinder might have been repaired. No thanks. Again, this is just opinion/preference, but I would personally opt for a used, running engine with a known history that had never been opened up or rebuilt. Rebuild it yourself or have it rebuilt by a reputable engine builder. That way you know everything started out original, and know exactly what new parts and machining went into the rebuild. You can also put in one of the vastly improved cam grinds that are available, and make choices like bearing type (I'm really liking what I'm reading about the new high silica bi metal aluminum bearings and their benefit with forged crankshafts. Or if you like Tri metal better... It's your choice, not just whatever is cheap that the reman shop uses. Also noteworthy that some replacement oil pumps are sloppy, have more play, and produce inferior oil pressure than the OEM pump it replaced. If the OE pump is tight, leave it alone! Transmissions IMO are even worse, because they are virtually always run to failure. If you decide to do a reman transmission, I would not settle for anything less than a Jasper, which has an extremely good reputation and a kick a$$ warrantee to back it up, but prepare to pay big for a ZF... And you will need a core. Again, I would look for a good running OEM and have a reputable shop work on it if and when it develops a problem. Ok. That's my opinion, and I'm going to duck now as I'm sure all those with glowing reman experiences are ready to tell me I'm full of it. LOL

 

+1 for having a good localish builder do the engine if you cant do it yourself! that way you know EXACTLY whats going on in there. I would also look for someone that has experience rebuilding DIESELS and not race gasser engines. I mean the basics are the same but there may be certain particulars that must be adhered to for these engines (the grit of the hone for example?)