Dear Tom;
This is typical of 'mainstream' auto people etc.
The costs are a BIG factor too, as there's about $2,000.00 in just the parts involved, with the crank & pistons about half. Plus a lot of special machine work ($1,000+/-) for the block/head. It's easy to get 4K in one these days.
Simple logic tells most "why bother" as a SBC 400" (used running) is $300.
I have several 'in the works' but doubt now with gas @ $3.25 they will ever sell.
Call Patrick's & see if he has some +.125 (flat) pistons (cast) for the 261. Add his F-290 cam & just "go with that"....
BTW: I'm 65 this year & started doing this in l954.
Good luck.