Firewall screw sizes

[westcoastdodge]

hi guys hows it goin,would anyone know the correct screw size for the voltage regulator and resistor fitted to the firewall of a '68 charger rt,think someone must have forced larger screws/bolts in at onetime.
circled holes shown in pics,thanks again guys.

[Nacho-RT74]

head is 3/8 as far I recall

[Nacho-RT74]

plated 1/4” anchor-headed screws

https://www.ebay.com/itm/Mopar-ECU-Electronic-Control-Unit-Mounting-Bracket-NEW-/401766543038

ECU uses same than resistor and regulator

[westcoastdodge]

just the info i need,cheers guys,stay safe

[gtx6970]

Im not 100% convinced ALL the 68 and older cars were a 7/16" hex size bolt with a free spinning captive washer
I pulled a bunch off a 1968 coronet a few years ago and they were all 1/4-20 thread pitch but a smaller 3/8" hex with a flat washer molded in the head

head markings themselves will vary plant to plant , year to year and model to model.
some were a N, some AF, some a series of circles

[westcoastdodge]

ah so they are supposed to be 1/4" 20 unc i presume,if so these holes are now to big,will have to get a couple of correct size nuts and weld those to the back of the firewall
would this be a good idea??
cheers guys

[gtx6970]

ah so they are supposed to be 1/4" 20 unc

Yes,
If you can get to the back side of the firewall with a dolly you can use a small hammer and flatten the metal out to regain the correct diameter.
or take a welder and tack a small portion of the hole closed

[Nacho-RT74]

once the metal is bent if you hammer it from back will back to its position but is already weak so will go back easilly.

on my 74 I opened slots on a side to insert U nuts and my ECU is attached to U nuts, but sure the area is flat.

[westcoastdodge]

cheers for the reply's guys,car is completely stripped so can get behind them no problem,will clean the enlarged holes  up  and weld the nuts on the back