The Ishipores are not conversions of existing guns. They where made from the ground up as a .308. Also they were never a stop gap invention until they could get better rifles, the army already had the Indian version of the FAL. The Ishipore was used mostly by police and rear units.
I have one, I like it. It isn't pretty, but it is under $100 and it shoots well enough, and is chambered in a very common cartridge. I have never had any thing break on mine yet, and I have never had any failures to feed except for one really badly mishapped CAVIM surplus round. I blame the ammo for that one.
Supposedly these rifles have the best metelurgy (sp?) of any of the Enfields.
The biggest advantage of the British .303 MkIV is that it has a better rear sight (peep) as opposed to the Ishipore which has a shallow V type notch. I like them both.
If you want a .308 get the Ishipore, if you want better sights get the Brit. They are both great values.