How is the master cylinder to pedal pushrod assembly ?

pics please.

What's the original pushrod lenght?

how it keeps in place ? just bolts to the Z pedal linkage and keeps loosen on master cylinder side ? Nothing more to hold in place ?

(as you know) remove the short thru bolt that bolts the horizontle pushrod to the brake pedal & unbolt the booster at the firewall & remove the whole assy. Bolt the MC to the firewall & iirc you would add new bolts (4) in from the back side of the firewall then butt the MC to the firewall & secure it with nuts on the bolts. You might just get the adjustable MC pushrod (MP) to head off any issues there as there are different lengths of manual pushrods (I've seen two). the MC you use must have a shallow recess in the tapered thimble hole in the rear of the piston in the back of the MC for the MC neoprene retainer to lock into. Some rebuilt MC's come with the retainer in the box but if not then cut a piece of vac line just long enough to fit the groove on the round nub end of the pushrod and cut a shallow groove lengthwise along its length so air can excape as you lock it down into place. I'd cap the MC ports & lock the pushrod/retainer all the way in place in your vice ahead of time.get the right bore dia and bleed the MC out first after it is on the firewall. Not sure if you need a manual brake pedal or if you can redrill another hole in the power pedal. EDIT in your vice with the kit of (2) blue square fittings/short rubber hose (bleeding kit) you could bench bleed it & lock the pushrod in right there & be done with that part

so, the only thing what keeps the rod into the MC piston is a neoprene/rubber piece installed by pressure into the piston ?

hole to rod on pedal link, I don't think will take care of that. I know pedal rate is diff between powered and manual brakes BUT MC being used is a diff one, not the stock one, so will check for brake quality once installed and will revise the brake pedal ratio later ( if really needed ).

Somewhere read these links are around 6.5"... so PROBABLY will build an adjustable rod with that middle measurement and maybe half of inch threads to each side.

(1) correct (2) clarify what you are asking

Only thing you need is the correct manual brake pushrod, or an adjustable one. You can keep the stock master and unbolt it from the power booster, and then remove the booster and power booster pushrod and bolt the original master cylinder in place of the power booster. The same brake pdeal assembly can be used. I personally did this swap many years ago on a 73 Dart Sport. Had power disc, just removed the booster and kept the same master cyl and just changed the pushrod. A pushrod from a manual disc or manual drum brake 67 - 76 a body are the same. The master bolts onto the studs coming out of the firewall in place of the standoff brackets on the booster diaphragm.

ok, nice to know. Is just that the guy who made the conversion ( is a friend of mine car, not mine ) built his pushrod and if he pulls out the pedal brake against the brake light switch the pushrod allmost leaves the MC piston hole. Is scary. I though it should get some kind of retainer or positioner to keep it safe in place.

Robert, What I meant is the guy doens't care to change or open a hole on pedal brake linkage to change the brakes linkage rate, since he feels the brakes fine with the same power brakes rate on deleted booster assembly. ( sound better now what I said ? ) he also installed rear disc aseembly ( dunno from what car he took, I guess some Ford ?

yes you need the snip of vac line to be slid on the machined smaller diameter at the rounded end to keep it locked in Plus the MC rear piston must have the recess about halfway down the piston tapered thimble for the neoprene retainer to lock into. A PB setup can use a MC with or without the recess so his current MC may or may not be acceptable to use in a manual brake app (if it has the recess he's good assuming the bore dia is OK for his app). He may need a longer pushrod so that the pedal height is normal and it makes the pedal vertical arm contact the light switch nub. As you know there is a little bit of adjustment in the brake light switch but the pushrod needs to be very close to the correct length.