Manual b body pushrod and A body MC for power brakes?

Can i run a 73-76 A body MC for power brakes using the 69 B-body factory manual pushrod?
I have noticed that the MC hole diameter is a bit bigger and the pushrod ,even with a new rubber on it, does not enter there under pressure .
I don,t know if this could be dangerous or will not work properly.Once everything is installed does not seem that it can scape,but it is best to make sure.

Thanks

I'm using an "A" body dual master cylinder on my Polara front disk upgrade. Although mine is a non power unit I believe the pushrods are pretty much the same and the opening should be the same as well. That said, the easiest way I've found to get the pushrod to seat in the master cylinder is to put a little grease on the rubber and push it in. It might take a little effort but should slide in eventually.

I was in a mistake.
The pushrod keeps pressed in this mc too.
The grommet is loose until you press it with the pedal a couple of times.
Thanks.