Can't immediately help with wiring - but first off....just checking the obvious first ....an "RVI" tach will work with points but not electronic ignition (you'd need either a converted RVI or an RVC tach...).
Can't see from pics but on most (not sure about this one!) smiths guages the bezel is held on by lugs and associated gaps in the casing so a firm grip (i.e hands) on bezel & casing and twist to match lug to gap normally sees them free in order to clean..... beware through the sealant used to keep dust / moisture & rattle free has normally set solid (looks like tarmac) and has gone brittle with age - carefully remove...... a hardeneing gasket goo like hermetite normally does the trick...