No one can tell you in advance whether your funds are "substantially identical stock or securities" within the meaning of 26 USC § 1091.
In most areas of federal law, if you are interested in embarking on a questionable course of conduct but you are not sure whether the proposed conduct is lawful, your remedy is to commence an action for a declaratory judgment against all interested parties. 28 USC § 2201(a). Prevailing in such an action results in "receiving a court's imprimatur to engage freely in what otherwise might be characterized as dubious behavior". Penguin Books v. Walsh, 929 F2d 69 (2nd Cir 1991). An unfavourable decision can be appealed. 28 USC § 1291. Further review can be sought in the Supreme Court of the United States by way of the statutory writ of certiorari. 28 USC § 1254(1).
Each step in this process results in the creation of written decisions, freely available to the public, which provide insight into the meaning and application of the law, and often act as precedent for future cases. This is all achieved without the plaintiffs having to engage in the questionable conduct before its legality is conclusively determined. However, this procedure generally does not apply to tax law because the declaratory judgment statute on its face excludes its application "with respect to Federal taxes", except for some situations not applicable here. 28 USC § 2201(a).
The IRS has developed a system of private letter rulings for obtaining advance tax advice, but this system has some major differences from the declaratory judgment system. For starters, the IRS has "broad discretion ... to revoke a ruling retroactively" to the detriment of the taxpayer who obtained and relied on it. Christy & Swan v. Commissioner, TC Memo 2011-62, p 8. The decision of the IRS to retroactively change a private letter ruling can only be reviewed if the IRS "abused the discretion vested in [it]". Automobile Club of Michigan v. Commissioner, 353 US 180, 184 (1957). Moreover, letter rulings are purportedly not precedential and "[a] taxpayer may not rely on an advance ruling issued to another taxpayer". 26 CFR 601.201(l)(1). Even more emphatically, "a written determination may not be used or cited as precedent". 26 USC § 6110(k)(3).
You can solicit forum opinions on whether those funds are "substantially identical stock or securities" but the answers are unlikely to be of use to you. All you can do is take tax positions that you feel comfortable defending in a court of law, if challenged.
