The stock push rod will work fine with the older M/C, the issue is when you convert to the newer two bolt M/C the adapter moves the M/c out from the firewall about 3/8"- 1/2" and that causes the pedal to be about an 1" or more lower than it should be which interferes with the brake light switch and the amount of travel you have with the pedal.
The safest way would be to get two push rods and cut them down so you only have one weld but you can get the adjustable one for about $30-$35 from someone other than Mancini.
For those that are trying to keep their original brake lines, WHY?
Brake lines are cheap, $2-$5 each at O' Reilly's or Auto Zone. The original ones are 30+ years old and may look good but it is common for them to rust under the spring and fittings where you can't see it and then when you have a panic stop they will blow out and you end up with a wrecked car just to save a couple bucks for brake lines and a little time to fit them. This is not the place to take short cuts, I've had brakes line blow out before and it is not fun going through an intersection looking and hoping you don't get plowed or wondering if the guy in front of you is going to stop before you can get your car stopped.
I don't see the point in risking your pride and joy or someone Else's or worse like someone's life over a little thing like brake lines.
I was at a show last night where a beautiful Charger went through a fence and down a hill, I don't know if it was the brake lines or the throttle stuck they were telling us both stories but it still shows you what can happen.
