All the accessory brackets will fit from your current mill - because when you yank an engine and stuff it back in you don't normally do it with the power steering, alt, vacuum pump, and fuel filter hanging off the engine - because with these off the engine and laying on the inner fenders it just give you more room so you will be bolting them back on anyways... But even then the brackets are interchangeable.
The outside of the block and heads have all the same size bolt holes as that found on the 7.3. The only difference is inside (bore, stroke and precup size) - they use the same injectors, they use the same size thread / pitch on the glow plugs. The differnece with the glow plugs is the terminal on the glow plug it's self (spade vs round stem).
Trust me it will fit and with no extra effort on your part. The bellhousing bolt pattern on the 6.9 to the last 7.3PSD were all the same so bolt up will be fine. All the IDI's (69 and 73) use the same motor mounts.
Basically it's the same mill just a tad bit less power - which you can't tell from the the seat of your pants and you would have a hard time on a dyno even. The upside to a 69 is it's cylinder walls are thicker so it's much much less prone to cavitation failure. You would not believe how many 73's have failed for this but 69's you don't hear about it because of the thicker walls. The biggest difference between a 73 and 69 is the injection pump - the pumps are interchangable (bolt for bolt and size for size) but the 73 is calibrated to flow more fuel. So if you stuffed a 73 pump on a 69 it would have more power but if you turn up a 69 pump you can get to the same level as a 73.
Heck I looked at stuffing a 69 in the Enterprise at one time but didn't do it because I ended up selling it off (last time I blew the engine up) I don't know what Freight had put in her but I do believe he went with a 73 he had laying around.
