Hmmmmm,
Is it weaker? Most definitely.
Now the question becomes:
"Is it weak enough to be dangerous?"
That's tough. I'll answer with a qualified no. Here's why:
There has been tons of discussion about early Springfields and their heat treatment. It has been pretty well established that the early ones were brittle, and could/would shatter, due to improper heat treatment. SOME of those have been re-heat treated, and some haven't. After a point (generally accepted to be between serial number 750,00 and 800,000 at Springfield and by serial number 285,506 at Rock Island Arsenal), the actions were more properly heat treated, and are now deemed "safe". So much from the brittleness issue.
Then there is the issue of the holes drilled in the front ring. Due to the fact that there are three drilled and tapped holes, I would guess that your receiver doesn't fall into the brittle group. That would be a JOB, and would likely have cracked the receiver. Of course, it could have been spot-annealed, and could still be brittle! But let's suppose it isn't. The three holes have definately weakened the front ring. The hole in the upper locking lug abutment is probably the worst. However I have seen dozens of rifles drilled like this with no aparent problems. Some have been chambered for cartridges I wouldn't even put in these old actions at all. Still they survive (amazingly), with aparently no ill effects. Some folks are lucky that way.
One thing to remember, is that the top lug is only half of the lock-up. There is another lug on the bottom, doing the same job. Also, there is the third, or safety lug, that protects you too. That's my take on the hole(s) issue.
Lastly we get to the main safety factor. That one is between your ears. This action is likely nearing 100 years old. Just how much pressure do you want to subject it to, with your face planted right behind it? It is not "modern technology steel", and pressures for the 1903/06 30 caliber cartridge were quite mild, by today's standards. Use some sense. Work up your loads with a chronograph, and keep them within reason. Velocity equals pressure. Enjoy your rifle, but don't "push" it, and you should be as safe as this somewhat risky sport allows.
Of course this information is worth about 50% less than you paid, and I categorically deny any and all liabilities for any actions taken by you or your agents, bystanders, lookers-on, or anyone else in the known universe. Gotta have deniability!
Oops, I almost forgot. An excellent paper on Springfields:
Springfields 
