Plumbing – New residential toilets all so tall

I was about to upvote the answer of @GreyBeardedGeek , because in general trying to find a match will be impossible. But then I read the word Toto. Toto is a different case: they have a corporate sustainability principle. The short answer is: call Toto at 1-888-295-8134. As for gaskets: one should come with the replacement tank, else is easy to get at any hardware store. Some PTFE plumbers tape is good also, if the supply line nut is metal.

And check the warranty also, it may apply depending on who you talk to at Toto:

TOTO warrants its residential faucets, bathroom accessories and cast iron tubs, excluding the acrylic side panel and accessories, (Product) to be free from defects in materials and workmanship during normal use when properly installed and serviced, for the lifetime of the Product from date of purchase.

The only real gotcha in this job is "don't drop anything". The tanks are made of ceramic and crack easily (not to mention do a bang up job on toes).

The only real gotcha in the warranty is that it is nominally non-transferable.

Not only is it ok, but Fluidmaster gives instructions on where and when to cut the overflow tube, as the follow photo shows.

Fluidmasters Article states the following:

The most important part inside the tank is the flush valves "overflow pipe." The overflow pipe is the safety net for your toilet. When properly set it will prevent water from overflowing the tank and flooding into the home.

The four critical areas of a toilet tank are:

1. The Tank Lever Hole
2. The CL (Critical Level) Mark located on Fluidmaster's fill valve
3. The Overflow Pipe (top end)
4. The Water Level

The water level should be indicated by a mark or (depending of the age or use of the toilet) a water stain on the inside of the tank. When rebuilding a toilet it is very important to set the fill valve to achieve this height.