IF this is a street car, how loud do you want the exhaust to be? Pick your mufflers & determine how stock you want the exhaust to be. Unless this is an all-out track car, I'd bet your Jegs headers are just fine (assuming they fit without too much issue).
I'm personally not concerned about "being original", but you can get 2-1/4" reproduction tail pipes & mufflers from Walker pretty cheap. They're quiet-ish & what I'm running now. I put the headers on myself & had a muffler shop make a couple pieces of pipe to connect the headers with the Walker tailpipes/muffers.
Before that, I ran "pigtail" exhaust with Hush Thrush (or any brand) of "turbo mufflers" which are pretty loud. The pipes bend out (preferably at a 45-degree angle instead of 90-degree) right in front of the back tires. This is the cheapest street-legal exhaust. Cherry Bombs are super loud & would fit in there too.
There are more "up-scale" mufflers out there (cost more, but "might" perform better). You can buy or have a muffler shop build you a cross-over pipe. If you don't sit in traffic (exhaust fumes), don't care about noise & don't have to pass inspection, then "dumps" (aka header mufflers with just about 6" of turn-down pipe) is the cheapest.
As for installing headers, get the car WAY UP in the air, even higher in the front, and expect to have to unbolt the motor mounts (normally just one side at a time) to wiggle the headers in from underneath. Header bolts instead of the studs help with clearance to get the headers in. Also, with headers, you can cut down the exhaust manifold studs about 1/2" which also helps with clearance getting them installed.
Hope This Helps.