[5150.4.67]

Wow, 375hp from a 305 might be a little high estimate. Ditto for 22mpg. The problem with the 305 is the small bore that restricts you to small valve heads and therefore less flow, not to mention valve shrouding...... now a big cam is completey out of the equation.
About the only decent head for a 305 (without breaking the bank) is the l98 aluminum head. It still retains the 58cc chamber.
Just speaking from experience: I built a mild 305 with 4 barrel FI and Megasquirt and when I was done I was happy. Then it wore off 2 days later and I said to myself, what the hell did i do that for? I could have spent less money and had 50 more hp with a 350!!!
Its fun to be different, but if thats the case, keep the 305 v6. Think of it as half of a GMC v12! (which it kinda is......)

Good luck and have fun!

And welcome! You will learn much here!