I know it's a couple of K over your budget, but this is what I'd be going for...
https://www.ebay.com.au/itm/1954-Pon....c100005.m1851
I know it's a starting price, but nobody will bid on it. In fact you my be able to contact the seller in a few weeks and offer 10K or less and get it. I bought my Trans Am for 6.5K with a RWC and it was in Unique Cars mag for months at 15K.
Oh and the 301ci to 455ci are all essentially the same block. just differnt bores etc. Easy to power up.
Just another option.