70's Alvarez 5034 bridge replacement (?)

I did this very thing with my old Alvarez. Turned out great. Kind of a midrange sounding guitar. Lacking in bass resonance and high end clarity. Very prominent in the midrange.

 

That is actually a fairly common modification but there are some things that look. First, all of the ones that I have seen have been compensated (set at an angle) - yours is not. However that can be fixed when you do the modification. Second, the ones that I have seen have a metal insert that carries the saddle and usually has two thumb screws that adjust the whole assembly up and down (that was its selling point) - I would expect to see holes at the end of the slot or at least indentation in the spruce.

There is one that I modified. Starting, you can see that the slot is angled, has holes in the ends and does not go thru to the spruce



The slot is filled with a piece of rosewood



And a new slot is routed at the correct scale length plus compensation



Finally a new compensated bone saddle is fitted



One other possibility is replacing the entire bridge with one with the proper slot. A premade bridge would not work on my guitar and I just didn't want to go thru the work of making one from scratch. I don't think it would work on your either because of the curve in the pin holes



The last possibility and honestly a pretty good one it to get an oversized saddle blank and make a super wide saddle that is properly compensated.

I'll add one more thing - with the other problems and probability needing a neck reset it might be a lot of effort for a guitar that isn't worth it. I always try to fix a guitar when I can, you'll have to make that call

 

That adjustable bridge idea cropped up on a number of guitars during the '70's - it was a good idea, gave the player an easy way to adjust the action both up and down (its pretty easy so sand a saddle but hard to un-sand it). The feeling is that it was a tone suck - all that mechanism resulted in a poor mechanical connection between the string and the top. I have removed a couple of them like the one in the pictures and assuming the old bridge hadn't been lost like yours I always gave it to the owner. In theory the guitar could always be put back if wanted.

Fixing up an old guitar is always a crap shoot - I do it for practice and experience and I frequently give the guitars to our school music program. But the things you list - pins, strings, tuners - might be the least of your problems - if the neck angle is bad then the guitar is more or less toast (or a good candidate for a budding luthier to practice neck setting).

Good luck, let me know if I can help

 

The foreleg of a sheep dried is the best nut or saddle material period, you should drop another saddle in it and it will have a lot of room for intonation adjustments, don't worry about it touching the top, it may sound better!! It certainly will sound better than the original idea, I remember those Tone Suckers !!!

 

It bothers me a little that I'm pretty sure I'm seeing the top through that bridge rout. I'd guess it was a kind of adjustable saddle that operated against the top of the bridge and not inside the cutout (as the other pic, which does show bridge wood at the bottom).

I would check out the neck angle and fret condition to make sure this thing is worth the effort.

A piece of bone to fill that hole is going to be a little hard to source. Even the wide micarta blank for the adjustable bridges isn't as long as that gaping hole. I would spend some time thinking about this - replacing the wood first is going to be a better solution, though will require a few more skills than just filing bone. Good luck!