Get someone to pump up the brakes and then try bleeding from the hard line on the chassis near the rear axle. If nothing there then bleed from the distribution block. If you do get fluid at the rear hard line, try the hard lines to the distribution Y on the axle housing. I'd bet the rubber line...
They should have dyno'ed it with the Australian 2 heads that are closed chambers. I'd bet they are within 10 hp of the twisted wedge heads for a whole lot less money. Also what about the CHI heads? They also make very decent power.
Either Duraspark conversion or a Pertronix drop in.
Personally the huge gm distributor is out of place on any Ford and there are better, factory appearing systems available.
Edit: checked your link and their "hei" is a small cap unit.
Easy to do this if your distributor is worn out. If yours...
As I recall, the hardened seats weren't installed until 1975 when they switched to unleaded at the pumps. Your machine shop might have put hardened seats in your heads when they did the valve machining. Check your invoice perhaps?
That's what the vibration is, definitely! Looks like you got the late model 50 oz. balance flex plate when you should have the early model 28 oz. balance plate.
Schwinn Stingray! With a Banana seat and a sissy bar and Ape hanger handlebars!!! Loved those things! I remember building bikes in my younger days. changing all the parts around, swapping cranks, etc.
Stock bolt length is 5.5" on my 73 351C-2V, UHL (under head length)
5 inches for the alt, bracket and spacer and 1/2 inch for thread engagement in the head bolt hole.
In the top picture of your left side, the wheel cylinder cup looks wet with brake fluid, indicating a leak. Might be a stuck piston and not applying, there by applying no brakes on left side and all brakes on right.