Will a take down 30-30 barrel fit my take down 303 Savage frame?

It should. The cartridges are near twins. I make .303 cases out of .30-30 brass to shoot in my .303 M99 TD, they work fine through the magazine. Just run a .30-30 case through a .303 FL die. A little difference in base diameter (.303 is larger) but it works.

I do the same thing, I only have 60 303 brass, have a couple
hundred made from just FL resizing 30/30s in 303s die. I get
a tad of corragating at base of neck even with annealing but
they work fine and have been loaded at least 3 times since 1x
firing.

This is a bit like asking if a cylinder from another S&W revolver will "fit" yours if the random cylinder came from the same Model and caliber S&W. Like S&W cylinders, Savage 99 take down barrels were not intended to be drop in parts. You'll be lucky if gunsmithing is not required.

My experience was that to shoot accurately the barrel has to get hand tight when rotated to the point where the key slots align. If it passes that test then it is time to look at head space. If I could not screw the barrel into my 99 before buying I would assume gunsmithing would be required.

By the way, early take downs could be dissembled with a 90 degree turn but latter ones could not.

Thanks for the help and advice.
Regards Dr Charlie

30-30 will work in the 303Sav rotor and cartridge guide that already exist in your rifle.
You can verify this,,and should,,by loading 5 30-30rds into the magazine and then working them through the action.
When chambering the 30-30rds,,just short chamber them and then extract and eject them if they don't quite chamber in the 303S.

A Savage 99 TD bbl will have square threads on it.
Later 1960's and onM99 production used V threads but the TD action was gone from production then (early 1940's).

The earlier TD used a 1/4 turn and release thread..later a full turn thread as already mentioned.
The 1/4 turn threaded bbl and full thread bbl should interchange on either frame. You'll just have to turn the bbl in the full rotations to seat it as appropriate.

Some things to watch for.
One is that the bbl when it comes around to line up the key slot,,it should be snug at that point. If it goes past that point,,you have a loose bbl and you'll need some gunsmithing done to make that bbl fit the frame.
You can't make the frame fit the bbl as then the orig bbl won't fit right.
Any fitting done here can effect headspace which is something unkn anyway till the bbl gets installed and locked into position.

Two is that with any orphan bbls that you may find,,make sure they are the same bbl weight & contour as the orig 303S on the rifle (featherweight,,medium weight,,)
The original forearm you have needs to fit both bbl contours or you'll be looking for another TD forearm also.

Three is that forearm,,it already fits the orig 303S bbl and locks into place with the latch.
When the new 30-30 bbl is on the rifle,,the forend may not latch into place as the forend hanger on the new bbl is off a tiny bit in size and dimensions from that on the 303S bbl.
You have to make the bbl hanger fit the forend,,not the other way around. Don't do any filing or alterations to the latch on the forend or it won't fit the 303S bbl right.
Make any adj to the hanger on the bottom of the 30-30 bbl.

...and try not to use the square hole in the block inside the forend as leverage to unscrew a stubborn bbl from the action,,or to tighten one up.
Yes that was the intended purpose of that little feature, but it has lead to more cracked Savage (18)99TD forends than I'd care to see.
The TD system is simple but flawed IMO. No takeup built in, no way to adj it.
Once it's loose, things like string in the threads, glue, solder, peening, ect start to show up in attempts to tighten things up.
Use it sparingly if it is tight yet and it'll last a long time.

If you are tempted to make your own .303 Savage cases from .30-30, I'd suggest you cut some 1/4" wide strips of masking tape about 2" long. Wrap those around the cartridge case base just above the rim. That will act as a centralizer for the first shot and allow uniform expansion of the case into the larger diameter chamber. Then remove the tape. If you reload, any .30-30 data will be OK. As previously stated, I would want to try a .30-30 barrel in my action before buying it to be sure it screws in properly. If your purpose for getting a .30-30 barrel is for better ammo availability, I suggest you take up reloading, form your own .303 brass, and continue using your .303 barrel instead. That way you know your barrel will fit and there can't be any headspace problems.