Re: budget engine/trans combo.....specific please
If you want LOW cost, I hate to say this but look at getting a GM crate engine. They're a dime a dozen and I'm sure someone can hook you up with a bell housing to mate up with a transmission of your choice.
I had an old C1500 '90 rwd 5.0L. I swapped out the stock engine for an upgraded 5.7L V8 with 320hp at the crank, going through a NEW, upgraded GM 4 speed auto. I'd say it put down around 230-240hp at the wheels. Total cost (engine was on sale) was just under $7.5K. That was a GOOD PRICE, especially in Canadian dollars. If I wanted the 350hp engine, I'd have to tune the suspension and other components to handle the extra oomph, and I'd be well over five figures. So 320hp crate engine worked for me. I put on 62K in two years with it and sold it for good money, I didn't see any profit, but came close to breaking even since I paid $2500 for the truck at auction with NO rust.
I looked at getting a 408 stroker for my Dodge Durango as it's my work horse; trailer puller, trail rider, etc. Best price locally I can find with a rebuilt block was in the $6K range, including the stroker kit. That's not including the transmission upgrade which I would have to do, so add on another $3K. $9K for a STROKER. That's too much so I decided against it as I'll be literally throwing my money away. The current 360ci V8 still has plenty of life left in it anyway.
As for the build you want, you're best bet to stay within your budget is to keep an eye on salvage yards, and Ebay. Ebay is a good resource to check for this type of stuff. A lot of times people will list something without knowing its value, and you could get a $10K engine for $3-4K. I don't see it often, but they are out there. NV4500 is a good transmission all around, and parts are a plenty. I'm not sure of the torque capacity but finding one in decent shape will still cost you a pretty penny, but not as much if you were to buy new.
As for engine internals, I wouldn't worry about upgrading the pistons unless you plan to boost the engine, either supercharger, turbo or add NOS. Stock pistons in nearly every engine are well built to withstand additional power within a reasonable means. My Dodge 360 block can handle close to 500hp before internal modifications are necessary. It's one of the reasons I bought it over a newer Ford or GM SUV at the time.
You can get creative if you put your mind to it. Thirty years ago, import sports cars had plastic rear differentials (most were covers) to save on weight. If you can get an engine with decent HP at a low price, just concentrate on weight savings and you'll gain performance that way. It costs nothing to remove bits and pieces, but costs a ton to add some on.
'11 Ram Quad Cab 4x4 SXT 5.7L HEMI (stock); 48,500m
'06 Pontiac G6 GT 3.5L 220hp; 64,000m
'12 Chrysler 200 Limited 3.6L 283hp; 28,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!