OK, here's the deal:
The correct marine 370's (the ones the Piers Harry spent the time to research and then match groups of 6 together that flowed close to the same amount before shipping) were the bomb years ago. Since then, everyone and his cousin's uncle's dog's neighbor has been selling "marine 370's" with predictible results. There are several different "marine 370's" made by Bosch and if you get the wrong ones, they aren't as effective as the injectors that PDR sold and even those did haze at idle and smoke more at higher loads that what DDP sells now.
As mentioned above, the piston shape has a big effect on how well these work, if the fuel isn't going into the right place (a small target), you get more smoke and less power. Back in the day, the marine 370's were the only step above the 215's for good power without killing your milage.
Why do the 140's cost more to buy? It costs more to make them! Read some of the stuff Joe D has written about the manfacturing processes to make these injector tips. According to the latest TDR, DDP extrude hones the tips to get the right size. Bigger holes take more time and I'd expect more scrap if the hone goes bad on occasion.
The tip is the part they send money and time on, they will install new tips and pop test your injectors if you send them you old ones. I got a set of DD4 tips CHEAP last year, they had a sale.
Jesse, I'm not sure what you are doing to get your pump set up. If it has a couple hundred thousand miles on it, it should get pulled and set up on a Bosch test stand by a reputable shop (there are only a handful I'd trust). If your local guy doesn't want to use anyone else's injectors it's because he's not a dealer for them. Ship your pump to a real performance shop, you will have better results. After I had my local Bosch shop (they do tractor pull pumps) set up a 180 hp pump it only made 340 on the dyno. I sent my next pump out, I even built a little crate to ship it in. It was a huge increase but it hasen't been back on the dyno yet. The pump shop estimates 425-450 and it feels like they are right.
If you are just doing a plate and RPM kit, you can do them any time. It looks like you have an auotmatic, you really need a better TC, your stocker won't let the power out. I'd ditch the K&N filter too, they let dust in. Use a BHAF, they keep the air clean and if you cut the restruction gauge into it, you can tell when it needs changing.