Doing a build with a Schwinn 434 aluminum frame. Attempting to determine what headset will work. I already determined that 1 1'8'' doesn't fit (anyone in the market for a new un-used one:), also determined that carbon fiber fork I bought with the 1 1/8'' al steerer doesn't work) I checked the Schwinn 91' catalog specs but it doesn't provide details. The head tube is cupped about 1/2'' deep on both ends with a 31mm internal diameter. Does the inside recesses/cups indicate a semi-integrated headset? Thanks!

They didn't have integrated headsets in '91. They didn't use 1-1/8" headsets/forks on road bikes then either.
What you need is a plain old 1" threaded or threadless headset/fork. Probably ISO.

To start with, if it is the bike i'm thinking (looking at one picture right now) it is a thing of looking at the picture to see that it takes a 1 inch threaded fork and a 1 inch jis or iso (who knows) threaded headset. U need to measure the headset "hole" to know if it takes a iso or a jis threaded headset.

1 1/8 headsets and forks came up to the market maybe like 5 to 10 years after that bike went out of production. Bikes aren't mekanos my friend, just do your home work better and use a lot of common sense. Like for example why did u get a 1 1/8 headset and fork when clearly using a caliper or a measuring tape the hole diameter of the headset area is 1 inch? Rule #1, to measure the stuff before buying.

Good luck

https://www.nice****ingbike.com/2009/07/schwinn-road/

I'd be surprised if a '91 aluminum Schwinn used a JIS headset, but I'm not that familiar with them.
ISO headset cups have an outside diameter of 30.2mm while JIS are 30.0. If you can't determine which standard the frame's headtube was machined for, just take it into a good shop/framebuilder and get it faced to the ISO size. ISO headsets and forks are far more common.

Stupidity? I obviously wasn't thinking...Just finished checking out the Park Tool site, and it appears that this frame is 1'' JIS,(the bearing chase is 30mm),which in hindsight seems to makes sense, as I'm thinking this frame was made for Schwinn in Japan. FWIW, I'm not out to deprive my LBS out of business, just wanted to attempt to make a bike up from scratch on my own. And yes, MEASURE 2x, BUY once.......

U can get a shimano 105 or an old shimano 600 headset at ebay maybe? Those ones are inmortal!