It would be interesting to test this using the 2-c-c analogue I drew in the post above. It would answer the question I have: can the 2,5 dimethoxy 4 X phenyl substitute for the indole.
I think you drew it wrong. Or you mean the phenethylamine's phenyl substituting for the pyrrole part of the indole in tryptamine? I don't think it's possible, if you tried to make DOC overlap in the same way, the alpha-carbon would stick out to the other side.
I don't think it's that simple actually. Even if aromatic rings of phenethylamines and tryptamines interact with the same residue, I doubt that they perfectly overlay. There's a reason why tryptamines need tertiary amines for the best effect while phenethylamines tolerate only primary amines if they are to be psychedelics. And there's a reason why phenethylamines need to have their phenyl rings substituted to have affinity at 5-HT2A receptors and it doesn't seem to be only an electronic effect, these 2 methoxy groups actually seem to bind to two serine residues. But the electronic effect probably plays some important role as well. In both 4-substituted-2,5-DMPEAs and 4-substituted-3,5-DMPEAs the highest density of electrons is at C2, C4, and C6 of the phenyl ring (the summary effect of all substituents). In the study I mentioned in my last post 2C-I and mescaline affinities seem to decrease in a similar manner when there's a mutation at F340. Still mescaline may not be an ideal compound for the test, because it's a weak agonist itself, it's a shame they didn't test a longer alkoxy chain analogue like escaline or allylescaline. However, when you look at the most potent compounds from both groups, you can clearly see that 2,5-DMPEAs don't tolerate 4-alkoxy substituents as well as 3,5-DMPEAs do. Admittedly, there are two 4-alkoxy-alpha-methyl-2,5-DMPEAs in PIHKAL that are psychedelics - TMA-2 (4-methoxy) and MEM (4-ethoxy), but they're also amphetamines and their potency is far lower than their 4-halo analogues. Moreover, while in the mescaline analogues series allylescaline and proscaline are the most potent, the 4-propoxy-2,5-DMA (MPM) is definitely less potent than MEM. 2,5-DMPEAs and 3,5-DMPEAs are clearly different.
Anyway, there are various ways in which people tried to make phenethylamines and tryptamines overlap, but I think it's pointless to assume that certain atoms in 2C-X's have their exact equivalents in tryptamines because there are other factors at play. One theory was that C2 in 2C-X's corresponds to C5 in tryptamines and the 5-methoxy corresponds to the indolic nitrogen. If this worked 100% fine, 7-substituted-5-methoxy-DMT analogues would be as good as 2C-X's, but perhaps there is some steric problem. Perhaps it's actually C6 of the indole that corresponds to the para position in 2C-X's... But then there's some worry about 6-halotryptamines neurotoxicity.
In my opinion it's also possible that both the phenyl group of 2C-X's and the indole of tryptamines may bind to F340 but in such a way that it's impossible to correlate 2,5-dimethoxy substitution with any concrete positions of the indole of tryptamines. I'm sure we will know what's going on and how both phenethylamines and tryptamines bind quite soon.
Same story for the diethylamine/amide.