Circular logic pertains to a progression in logical steps which , at some point, returns you to the original point:
1. Upgrade the 305 buy means of cam,heads,intake,carb,headers and exhaust.
(Everything except the heads would be usable on a future 350.)
2.Have machine work dore on 305 block, but then you need new pistins,rings and bearings.
3.With expense now climbing, don't waste $$$ on the 305; move up to 350
4.Machine work, pistons,rings,bearings,cam,heads,etc.etc...........+cost of 350 engine now getting too expensive
5.Just upgrade 305 as per #1.
That is circular logic in a nutshell.
(Actually there are many more intermediate steps, but I get tired of typing.....)