The best No.4 receiver with the best quality bolt body converted to 7.62 NATO held up okay but was never subjected to the stresses of a Battle Rifle to the extent that the rifles of WW1 and WW2 were.
The 50,000 PSI of the 7.82 NATO exceeds the maximum allowable pressure for .303 ammunition by 2,000 psi, so it exceeds the safety limitations of the Enfields for extended use under expected harsh conditions of the field as opposed to the range and casual use with regular cleaning after relatively few rounds at any one time.
No.1 Mk III* rifles were found unsuitable for the 7.62 for good reason, insufficient margin of safety.
7.62 conversion kits were available at reasonable prices in the 90's, I considered getting one at the time. The reason these kits were available is that wide spread conversion of No.4 rifles was not considered to be a good idea in the long run.
Had I converted a No.4 I'd have used only handloads that generated pressures no higher than those of the .303 handloads I already used.
Whether the modifications made in producing the A10 clone of the No.4 are entirely necessary or not is a question of individual rifles and the quality of available ammunition. Dangerous 7.62 NATO shows up now and then even today, with pressures far higher than a No.4 should be subjected to.
The Indian rifles vary greatly in quality and condition, and I'd expect that the worst examples had been scrapped long ago and never made it to the surplus market. Any obviously defective Indian rifles should have been broken down for spares by dealers to avoid accidents to their customers.
If a No.4 or No.5 receiver can be spread by hard use firing .303 ammunition then how much worse might the situation have been when the ammunition generates higher pressures as a matter of course.