[Chuck78]

Makes me wish I kept that 73 Camaro 307 that came in my 71 former SS396 Camaro... I am appreciating good gas mileage efforts for my truck, which is my good weather daily driver, replacing my 89 Suburban with 350TBI and overdrive to winter use (5200 lb truck that gets 22mpg highway w/ 2.73's!).

Now, I've got a 62 GMC 305D V6, which has a reputation of being a real gas hog, and no hot rod capabilities really, but an awesome workhorse truck motor that will pull down a house. After some tuning, HEI upgrade, and swapping the worn out Stromberg for a 500 cfm Holley 2bbl, I am getting much better gas mileage than expected. Granted, I have to keep it at 60mph on the freeway to keep the rpm's down, but I am getting about 18+ mpg. I'd expect it to remain the same when I put in a Tremec 5 speed with OD, as the peak torque of the 305 is at a pretty low rpm, but then again, 10mph more wind resistance of my updated good cruising speed might drop it down a fuzz.

Back to the 307, since the 305V6 parts are mailorder only, and a total rebuild kit is well over a grand, I wish I had a backup other than a 400 sbc in case my 305D V6 ever had a fatal breakdown. It'd be nice to have a 305 V8, 307, 327, or 350 to put in the GMC panel truck as a backup if the monster 305V6 ever took a crap. As it is now, I am building a good stock on spare parts for the truck, stuff that I can't get off the shelf anywhere, and I might even throw in a set of motor mounts for an sbc into the parts bin for road trips "just in case!"

There's merit in these times to building a moderate engine that behaves like a V8 when you put your foot into it, yet can be very streetable and almost economical when you need it to be.
I am SOLD completely on the 96-99? GM truck vortec heads for this same type of engine build, if not any streetable sbc build really. I think they will work fine on a 307 (3.875"x3.25"), but i know on the smaller bore 305 V8 (3.736"×3.48") that the vortec's valves are a bit on the wide side for the the tiny 305 bores.
I think a small V8 like this is a great thing for a well driven vehicle that serves more of a purpose other than hot rod/pedal to the metal. GM TBI (older OBD-1 computer), a simple aftermarket TBI, or a well tuned Quadrajet (or off the shelf Street Avenger) would go great on an engine like this with an RV cam or mild street cam for a good running street engine in a truck especially. A 5 speed or 700R4 and this type of build could make quite a practical yet still fun to drive engine in a 3000-4000 lb car or truck.
If you notice newer GM small blocks have a tendency to have smaller bores and longer strokes:
293 = 3.779" x 3.27" ('99-later, Gen.III, "LR4" 4.8 Liter Vortec, 6.278" rod)
325 = 3.779" x 3.622" ('99-later, Gen.III, "LM7", "LS4 front wheel drive V-8" 5.3 Liter Vortec, 6.098" rod)
345 = 3.893" x 3.622" ('97-later, Gen.III, "LS1", 6.098" rod)
350 = 3.900" x 3.66" ('89-'95, "LT5", in "ZR1" Corvette 32-valve DOHC, 5.74" rod)

(as opposed to the 302/327/350 @ 4.00" bore and the 4.125" 400 sbc)

as the engineers have learned that they can get more efficient combustion out of a smaller bore with a good cylinder head design, but then again, you have to find a middle ground between the long stroke/small bore (w/improved combustion efficiency) vs the downfalls of the long stroke's much greater piston speed and travel (more friction). I think the friction from a larger bore (more surface area on piston-to-wall contact - with shorter stroke - less distance/vertical friction) is going to be less than a small piston traveling a much greater distance, but I think finding a middle ground is a good thing.

Also, one other variant on the engine geometry tweaking, goes against the smaller bore principal, but the LS2 uses the theory that putting in a really long rod helps power and efficiency a lot (hence people ditching the 400's stock 5.565" rods for the 350's 5.7" rods or aftermarket 6" rods):
364 = 4.000" x 3.622" ('99-later, Gen.III, "LS2", "LQ4" 6.0 Liter Vortec, 6.098" rod)