I was looking at buying the used Dan Heaton frame and a Koxx1 White widow seat…
Will the Frame fit on a 20" DX and is it strong and light?
Does the seat fit on the DX seatpost or will I need to buy a new one?
And Is the seat good and thin? (I was thinking of buying a Kh street saddle for SIF, but I came by this one)
Is this a good idea all together?
Thanks! 
Also, does the KH seat fit on a dx seatpost? Or do all seats have different posts…
I would suggest you get the KH fusion street saddle. Having the removeable cover is realy great. If you break your stiffner and need to fix it or if you want to upgrade to a CF base It makes it realy quick and easy to get your seat apart.
I can answer you one question here. Koxx saddles are awesome:D Nice and thin, but still comfortable, not to mention the looks;)
KH seats are near enough exactly the same as K1 just different covers. You need to decide wether you would rather have a seat cover that looks “better” or be able to easily remove your cover so that when you break your stiffner you can fix it or upgrade your base to CF.
Okay you will need a new seatpost if you get the frame…and am not possitive it will fit because DXs have funny sizing…but some Koxx frames dont fit a regular size so the frame might fit? But im not sure…
And the seat would be great…Because it looks great…and you wont break it for a while if you do…Ive got a KH Fusion Street and I havent broke it yet…It works great…So the seat would definatly be good.
Isaac
What If I only got the seat… Would I need to get a new seatpost? Or do all seats use the same post?
And I read that the frame uses a max 2.5 tire… whats the DX size?
You mentioned the 20" DX, which hasnt been made for years, so I am assuming your are talking about the 19" trials DX.
The DX uses a 2.5" Maxxis creepy crawler.
The DX and Koxx unicycles use a standard velo base. Koxx uses 27.2mm post size, and the DX uses a 25.4 post size, but the bolt pattern will be the same. So you would need to buy a new seat post to fit in the Koxx frame. They are cheap though. Only about $20. I dont know what the guy above was saying about DX having weird post sizes. 25.4 is a very standard size for seatposts.
The frame though, uses 42mm bearing holders, and the DX uses 40mm bearings. You will have to shim your bearings to get them to fit the frame.
The seat is thin, and id rather go with a KH cover so you could take it off and on easily, as mentioned above. Both seats are thin, curved, and comfy.
Would I need a new seatpost if I bought a KH street saddle?
No.
No I was saying that the frame…like fitting onto the bearings, not the seatpost…Because a regular size is 42mm Bearing…and the DX frame is ?.