Hey members are 14 inch rear shocks to long to mount on a 1977 MC-5.
14" will be fine, even 14-1/4", makes the bike turn much better.
Yes, they will work, but be sure to re-adjust the chain guide by the rear sprocket; as you lengthen the shocks, you are pushing the swingarm down, changing the angle from the stock shock length. If you don't change the guide, the chain will wear through the block quicker. And of course, you are changing the axle travel which can be an issue if you race AHRMA races....
1976 250 MC5 Original Owner
1976 Penton 175 XC
Can't remember the last time AHRMA checked my rear shock/wheel travel. Especially on a PV bike.
Pete Petrick
175 Jackpiner
Slow but Good