Chopperguy - nylon bolts and flatwashers are available and I would suggest using them. If there is a chance that they may keep your plane out of the dumpster, do use them!!

Here's a condensed paragraph I got somewhere about the H9 P-51: "Do not flex the cowling, the paint chips off, needs to be fuel-proofed and a cooling air exit. Engine mount bolts may extend beyond the back of the firewall and penetrate the fuel tank. The firewall is weak...cover the outside AND the inside (and check inside gussets) with a layer of 15min...I've heard stories aboout "separating firewalls", I epoxied the "joint" where the wing attaches to the fuse as well...(the piece with the blind nuts in it), be certain to reinforce the firewall to fuselage joint with plenty of epoxy.
AILERON SERVO BOXES: Two of the mounting blocks had broken free and a third was almost broken too, thick CA them then cover them with 6 min epoxy. After the second flight,the rudder servo blocks broke free.

The landing gear in the kit not strong enough for the tall legs of the Mustang. Replace it with 3/16" wire. Also, the retract servo needs to be elevated 1/4" to 3/8", or the servo can't retract the gear. "

I have a .050 titanium plate coming for my firewall. I haven't messed with the gear yet. And I haven't unwrapped the aft end of my fuse to start on the servos and horns, but I am planning on fairly massive changes back there, like pull-pull rudder and elevator and Robart retractable tail wheel.

Also planning on installing flaps if that is feasable without too much trouble. I haven't held the wing up to a light yet to see what is in there where the flaps will go.

I have a TruTurn spinner for four bladed props on back order so I may try the adjustable 4 blade prop system from:

Vario prop

or four individual wood props attached to a center hub:
Zinger
(13x6, #4133 prop $24, 3.5" spinner #6600 $24) ....if they would answer my email.