Just for fun decided to start using google on your behalf and came up with this
http://www.nostalgiaair.org/forums/M...1/M0108821.htm
This is from '70. Class B transformer coupled power amplifier - not exactly the stuff dreams are made of, but in yours it will likely have done away with the transformers and be a quasi complementary symmetry design, so at least won't be bandwidth limited by the transformers. Power output will be rather severely limited by the low B+ voltage though, this is after all before the days of BTL amplifiers, or switch mode supplies, and another limit will be the fact these old decks need 8 ohm speakers rather than 4 ohms.
What could cause dead radio here? I would start with cleaning the tape/radio switch really well, and in yours the AM/FM switch. Also, the 8 track player will definitely be wanting a new belt if it's going to work long term.. even if the existing belt still works, it will doubtless be stretched and not achieving the best possible wow and flutter performance, and nobody wants to be installing and removing head units unnecessarily if it fails in use.
If it's not switches, it will be failing coupling capacitors. I have had very little luck with low value electrolytic capacitors in audio equipment from before 1980 still meeting spec. You would probably want to go ahead and just change them all out. Not a bad job though, the new ones are so cheap all it takes is some bench time. Once you get the switches and controls cleaned, the capacitors replaced, and a new belt, then you have to go about adjusting the tape head so that it doesn't hear the wrong tracks. This seems to be the Achilles heel of the format, as soon as I get my home player adjusted for one tape, it seems all out of whack for another tape for adjacent track bleed through. Then touch up the azimuth for best high frequency response, and you're about home free.
Then hope that the splices in your tapes aren't dried out, because if they are, the tape will break at the splice and you will end up with a mess on your hands. I picked up a roll of 1/4" foil splicing tape at radio shack back when they still carried it, but probably now you'd need some kind of kludge to make it work, and every single tape will have to be done. They also will need new foam pressure pads (for the cartridges using foam pressure pads), else you will have all sorts of flutter related problems and drop outs unless the cartridge is inserted just so. And if the tapes use rubber pinch rollers as opposed to the later plastic style, then this may be another problem - if it's dried out then the tape can slip and again reduce performance.
Add to this that at this stage in the game, the lubrication which keeps the continuous loop moving along is likely getting old, and the tape can bind and, well, again reduce performance.
I think that the 8 track format can have half decent performance when everything is optimized and tuned and operating at 100%, but keeping it that way is a giant pain which crosses the line into "not worth it" for me, especially considering that 95% of the 8 tracks I come across are music I have no interest in.
Cassette on the other hand, while inherently limited by the slower speed, has the same track width as 8 track, and a much better situation in terms of maintainability and media availability. It's also nice that you can buy blank tapes any time you want, instead of trying to keep old ones together with spit and chewing gum, and suffering either constant failures, or a never ending maintenance nightmare as your collection expands.
I think the only situation in which I would want a functional 8 track player in my vehicle, would be a collector's car which originally came with one. For example, if I had the good fortune to own a '66 T-Bird, and it had the factory 8 track deck, I would move mountains to make sure it worked perfectly and I had the best 8 track collection going - as a retrofit though I don't really see it being worth the effort, especially since by the time your car was made, cassette was already starting to take over and 8 track was in terminal decline.