As the manufacturer was Royal Enfield, then that's what DVLA will have them down as. You'll need to provide evidence that RE manufactured and sold these bikes under the 'Indian' brand, (essentially as 'export only' machines). However, DVLA seem to be mostly peopled by simple-minded souls who are only capable of pushing buttons (frequently the wrong ones to boot ...) for items over which there is no possibility of confusion. Be prepared for a certain degree of frustration!
The REOC will be able to provide you with full details of date of manufacture, shipment, retailer, etc, so if you haven't already made enquiries, it would be worth doing.
I assume you meant to type in 'V5C' rather than V55?
If a US-imported bike came with it's 'pink slip', then DVLA probably would accord it as being of 'Indian' manufacture, simply transferring the information from one document to the other.
However, following the closure of the old LVLO's, if the bike has no such documentation and needs to be re-registered under DVLA's 'age-related' scheme, then the only thing they'll accept these days is a dating letter from either the manufacturer, or alternatively, one of their recognised dating authorities (such as the REOC). That being so, I can't honestly see DVLA accepting 'Indian' as the manufacturer considering their current approach and mindset.
Exactly so. Royal Enfield (Redditch) never owned the American 'Indian' brand, so could never have produced them under this name in their own right. Essentially, Tomahawks, Chiefs, Apaches et al are just re-badged versions of RE models with americanised fittings.
Thus, as Royal Enfield (Redditch) is the original manufacturer, any company dealing in classic insurance should be aware of this variation-on-a-theme and should be able to accommodate it without any problems.