Unfortunately there has never been a good 351c made in 1/25 scale. Many kits have this engine but they are generally inaccurate lumps of plastic in older kits (and several kits that claim to have a Cleveland or Boss 351 are actually a Windsor based blob). The Monogram/Revell 70 Mustang Mach 1 in 1/24 scale has a very nice 351c except the valve covers do not have the 'Power by Ford' script. Possibly the best option in 1/25 scale is the MPC 73 Cougar.
The 302 you mentioned is a very different engine than the Cleveland, except that the Boss 302 had Cleveland heads. The 302 is a Windsor engine and they are very different in the timing chain/water pump/thermostat housing area, and the cylinder heads are visually different, too (except the Boss 302 heads). The 302 is also physically much smaller than the Cleveland. However the 400 you mention is the same engine externally as the 351c.
If you were building a 351c for a racing or highly modified street application, the best starting point would be the engine from 90s era AMT Thunderbird NASCAR kits. These have the most accurate 351c heads in 1/25 but not sure if other parts of the engine would be suitable for making a stock 351c (very likely not). Mixing and matching the right parts from various kits will make the best Cleveland, but unless you know Ford engines well and are familiar with what is in older kits it could be a difficult task. Probably the engine from the MPC 73 Cougar is the best starting point.
There were (are?) a couple resin options. I believe the best ones were offered by Motor City Resin Casters or Scale Modelling By Chris (same product) and were available in two stock configurations, but I haven't seen these around lately. Try a google search and you may find something, or try ebay. There is another resin option but I will advise you to avoid it. It is a turbocharged street engine, seemingly copied from the MPC 80s Bronco, but that engine is a very poor substitute Cleveland (looks nothing like one) and is not stock anyway.
I hope some of this helps. In the end it largely boils down to how picky you are on accuracy. With valve covers and air cleaner housing of the right shape, a thermostat housing on the top leading edge of the block (instead of on the intake manifold) and some Ford blue paint....