Hhhmm? To quote Tommy Lee Jones in 'The Fugitive', this sounds a little "hinkey"! Frankly, I'd check with other suppliers.
You shouldn't have any problems installing a later-model intermediate band in your C4. However, with so many good, durable performance parts available at reasonable prices, there's little reason to choose a standard or 'economy' rebuild kit, even if you don't hot rod your car.
I've had good luck getting quality parts from Oregon Performance Transmissions, or even eBay vendors such as this one.

Fits Ford C4 Raybestos Red Performance Deluxe Transmission Rebuild Kit | eBay
Find many great new & used options and get the best deals for Fits Ford C4 Raybestos Red Performance Deluxe Transmission Rebuild Kit at the best online prices at eBay! Free shipping for many products!
www.ebay.com