Why not go with a stock 1bbl manifold and a Carter YF? There were a few of those made for the 250. You don't want to overdo things. There is positively no sense in running too rich and it is dead easy to do. Jerry and Jon have told you (very correctly) you need smaller...a YF 1bbl would do that for you and is an excellent design.
Now on the other hand if you want a brand spanking new 250 with spanking new manifolds and HEI, you can buy one and you don't have to leave Texas to do so:
https://www.donhardyengines.com/specials.htm (go to the bottom of this page)
You'll have to make peace with the EPA, but a brand 250 made by GM can be yours for $2300 or $2500. In my opinion that and a Carter YF would be as trouble-free as you can get and you will spend more than $2500 rebuilding one plus you'll have to watch the machinist like a hawk 'cause it ain't easy to find good ones today.
