i would just get a refund from jegs,and with some companies its better to buy direct like performance automatic.

not long tube but cheaper than most headers!
and probably good enough for 500 or so hp


https://www.autokrafters.com/product/24328/exhaust-manifolds-pair-1960-64-ford-galaxie-fe-engines-352-390-406-427-c3az-9430c-1f

i have had this for a long time so want to sell.this was purchased new in approx 2008  to do a t-bolt clone with the front and rear seats like original.i think the front are for a split bench seat but could be reconfirgued to the bostrum buckets.also a large roll of the vinyl in same color.asking $300 for it all.

new arp head bolts for fe $50

new edelbrock fuel pump  $120

also get good shocks and make sure your spring purches are not rounded and loose.one trick i did on my 68 fastback,was to use clamps on the front of the leaf springs.they worked really well,but also had stiff springs as well.didnt need any traction devices but that!

maybe they did that to lower the car as well.one mustang i had with fe big block and c6,had  big deep gouges on the bottom of the bell on it,and car 14 factory tires/wheels,so it sat pretty low.
in any case,if it was for 500 hp or more drag car i would not use it.ive seen what happens when a stock case bellhousing splits on the drag strip at 130,it destroy the car.it was a gm,so weak bell any way. so yhat must be weaker than stock.

i am surprised that you are using autolite plugs!i had many of them fail around 2010 and went to ngk and never looked back.

i see no reason why a mild build 427 r code engine couldnt be a reliable daily driver.its when you let them sit for a year or 2 that they start going bad,so better to drive them.after all ford did build them as a production car.like the boss 429 mustangs,they even crash tested a 69 boss and a 70 boss.but you have done a great job($) getting the car there.although i would be using an electric water pump an fans with no ac,power steering and no pwer brakes for my 69 sports roof.