If Amex is still holding a grudge from the past, you'll get a denial based on their internal data before they do a HP. If they HP and you get denied, it's due to something on your reports and not your past internal history. You could keep your reports locked and do an app if you're worried about a wasted HP and see if the decline letter states "previous unsatisfactory relationship" or "unable to access credit reports".
One thing Amex is known for is forgiving after being made whole again from unpaid debt on past accounts. You would have to decide if paying a $6K debt from the past is worth getting back in with Amex to you should it come down to this.
If it's not an internal data denial it should be a soft pull now. Amex just started doing applications with a decision based on a soft pull so no harm in a denial. You don't get to see your CL though until you accept and take the hard pull.
CL? on an amex? have things changed that much since Ive been gone? 
@fastboat wrote:When I was a freshman in college (early 90s) I got an amex card the day spring break started. Long story short I ended up having an account with a ballance of 5 or 6000 written off.
Since then I have been more serious about my credit. Currently experian has me at 755 right now, but one card I had charged up close to the max last month just got paid off and it will be reported shortly. When that happens I'll be at about a 7% utilization ratio with a collective credit limit of just under $100k. I have two primary cards I use with limits of $30k and $35k, and a few others right around $10k each. My history sees them all charged up to close to the max, then paid off, typically once or twice a year. Own a home, with no mortgage, make decent money.
I have tried to prequalify for an amex more than once, and no luck. Not even when my credit score was hovering at just under 800.
Is it likely that I have a lifetime ban, three decades on? Can I find out without a wasted hardpull? I'm specifically looking to get the platinum card for it's travel benefits. Anythign else wouldnt be useful to me.
TIA
No it's not likely that there's a lifetime ban.
If you want the platinum card, go for it.
If you want to have an idea if the past account is an issue with Amex do a soft pull application and see what pops up.There is a link floating around the forum -
EDITED TO LINK THREAD WITH SOFT PULL LINK
I did it last week for my father and past account history was the primary reason for denial. You will not waste a hard pull.
I had issues with Amex around 10-12 years ago for more than what they wrote off for you and this year I have been approved for a number of their cards both credit and charge. Although I know they havent completely forgotten the past as I have low SL and low international limits and low POT limit atleast I am back in the door.
@fastboat wrote:CL? on an amex? have things changed that much since Ive been gone?
Amex offers regular credit cards with actual limits, yes (in addition to their well known charge cards).
As a couple of others have alluded to, you can try Amex's new prequalify tool which should only be a SP regardless. If you're still blacklisted, it'll deny you and let you know.
@fastboat wrote:CL? on an amex? have things changed that much since Ive been gone?
The Platinum Amex card does not have a preset spending limit but several other Amex cards have credit limit.
@Inspiredman wrote:
@fastboat wrote:CL? on an amex? have things changed that much since Ive been gone?
The Platinum Amex card does not have a preset spending limit but several other Amex cards have credit limit.
This is a fallacy. One may find their shiny platinum card with a $695 fee to have a monthly limit of $500 or less if you've been naughty.