The straight 8 is a superior engine in many ways, so you would want to keep it, even though it is heavier and costs more to make.
Transmissions were not better back then, but not bad, so again you should try to keep the original. The only negative is that no automatics and non-synchro first gear. You can likely get any GM tranny and it will work. You may also be able to get a 60s transmission if the bellhousing is the same bolt pattern.
What you do not want to do is to mate components with a different bolt pattern, because then you would need an adapter plate, spacing could then be off, etc. Mixing an matching between engine and transmission is usually not a good idea. One usually keeps engines and transmissions paired. If I was going to upgrade something, it would likely be the differential. Back in the 40's they used straight bevel gears instead of hypoid, so they were weak and noisy.
Unless your building a hot rod, keep it original or you will never get the money you spend on this car back, Car collects always want the car to be as original as possible.
For collectibility purposes, you'd want to keep it original. However, if you pull the stock engine/trans (keep and rebuild at a later date) and drop in a Chevy 350 engine/Turbo 350 trans. combo and driveshaft, can be done with a minimum of fuss. Adapting newer engine to old trans maybe more bother than it's worth.
unless it's a station wagon, there is no way this car is worth the cost of either a restoration or a hot-rodding. This being the case, you have to decide on what basis you are willing to accept a huge loss of investment---that is, which path (accurate restoration or modding) would give you the most fun?
Personally, I'd hot-rod it, because, let's be frank here---this was an old person's car in 1946 and is no more exciting to drive now; but with a Chevy crate engine and modern overdrive transmission, upgraded brakes, tires, suspension and exhaust, aftermarket AC, good sound system--you could really enjoy this car---but that's a $35,000 to $50,000 proposition.
The only other logical path is to not restore the car---just get it running, safe and presentable.
Hey whats up people? In 2007, I purchased a 1946 Pontiac Streamliner and after 7 yrs of collecting enough money I finally threw my Pontiac into the shop. I have the original straight 8 engine and I am really thinking of restoring the engine, but my question is: what are the advantages and disadvantages of keeping the original engine? And would I have to keep the original transmission? Would I have to purchase a transmission within 40s-50s or can get a modern one?
