Instrument gremlins.

I'm not exactly panicing, because I have a lot of time on my hands with winter. So I'm in no rush. Plus I wouldn't doubt a few issues are coincidental. ( Because my speedo is also stuck at 25, and it worked before the engine swap.)
I have hardly any instruments working on the dash of my 1975 duster. I swapped the engine for a gen 3 hemi, wired the headlights for H4 bulbs using relays, I also swapped the column shift, for a floor shift column ( Norm's). and removed the seatbelt interlock system.
The car runs perfect. The fuel level gauge works pefect. The brake warning light works, as do the rear brake lights, key buzzer, and the headlights. The windshield wipers seem are a bit slow, but the windshield wash works. The directionals don't work, ( the socket for the front drivers side blinker is broke, but will take the bulb, and hold into the back of the lamp) The bulb on the drivers side, side marker is dead, or doesn't work, and the horn is a joke, almost non audible. I wired the violet wire to the temp sending unit, but it's not responding. the grey wire is waiting for the correct oil pressure sending unit ( the one I have is wrong, and for a gauge. ) The dash doesn't light up at night, no matter how I play with the healight switch. And either the previous owner has bypassed the ammeter, or it's dead too. It looks like the blinker, and horn relays are in place, but the car came with a 3 prong relay in the glove box ( Chysler pn # 93596-A ) Don't know what, or where it came from . I know very little about wiring, but I almost suspect the little voltage regulator, on the back of the instument cluster.
I have a set of 2 1/4" autometer gauges ( volt, temp, and scratch the oil pressure, because I hate the idea of oil lines in my interior.) Can the volt, and temp be fitted into the dash, where the factory amp, and temp are, or is the headlight switch too bulky to allow that ? Is the circuit board a major hurdle for soldering ? This is a hot rod not a resto. When I look at pictures of cicuitboards on google images, it looks like there maybe more than one circuit board behind the instrument panel, is it one piece or several ? I guess I would like to fit an volt, and temp on the left, or the instrument cluster, and a electrical oil pressure gauge where the idiot lights are on the right.
I'd appreciate any ideas. I do think the right side bulkhead connector on the engine bay side of the firewall is in bad condition. I have better connectors that I could replace that with, if all I have to do is some soldering. thanks.