The differences between the old and new Tri-X films are subtle.
I recently (2 years ago) developed a roll of 1981 Plus-X with a modern roll (which also changed). I used the same time in the same developer. Results were good with both rolls. (The old roll was well stored I suspect.)
As for D-76, the difference is agents that make D-76 mix more easily in varying water quality. Also, metol will not easily dissolve unless dissolved first. Ilford solves this problem in ID-11 (which is the closest commercial developer available to original D-76) by having the powder in two packages. Kodak solves it through chemical additives.
Both are good. I mix my D-76 from scratch, but when I bought it, I bought Ilford's ID-11 in preference because it is sold in Canada in metric measurements, and Kodak sells D-76 here in US quart and gallon packages.