When speaking in gen terms, the 5513 case differs form the 1680 case greatly, as the opening/aperture for the dial is smaller on the 5513. A gen 5513 has a 26mm dial, whereas the 1680 and 1665 have 26.5mm dials. As such, some reps may differ in this sense (the numerous models out there will vary), though the one consistent and firm exception to the rule is the MBW case (which is based on the smaller 26mm dial for both 5513 and 1680, thouch not accurate for the 1680).
When I built justasgood's 5517, it was based on an MBW 5513 case; the lug holes were drilled out much too large by a previous owner, and there were two choices: i) scrap the case and start with a new one or ii) drill the lugs out even more and have bars pressed in to make it a 5517. I chose the latter for his watch, to which jmb graciously did the lug bar conversion...
Before
After