Adding a 1977 factory tachometer to a 1974 gauge cluster

[Bryan74]

I am working on my 1974 1/2 ton 2wd pickup. I have read through almost all the previous post on this topic but I did not find a post that covers what I am wanting to do. I am installing a factory tachometer and I would like to get some feedback on my description plan listed below as to whether or not this will work.
My current configuration is 1974 factory gauges which include the amp gauge, mechanical oil gauge, temp gauge, clock, speedometer and gas gauge. I have a 1977 tachometer that I plan on installing. I will remove the clock and install a new gas gauge in its place. I will install a new 73-75 printed circuit panel for factory gauges with tach. Are there any other changes need to be made for this to work? I would appreciate any guidance.

[ccz145a]

I would hooked it all up to a 9V battery and test my choices before the smoke test.

[Bryan74]

Good idea, thanks for the input.

[ccz145a]

Yeah, I cobbled together '75 speedometer, fuel, temp with '84 volt, clock, and circuit board all in my '75 housing and kept the mechanical oil pressure from the '75. too. I just put 9v to the clock to make sure it worked, then got to thinking there's not a enough amperage to fry anything, so I tested enough circuits to convince myself nothing would burn up. My main concern was the section I cut out of the circuit board to make way for the mechanical oil guage.