Click on a pic to enlarge:

Click on a pic to enlarge:

Triangle shaped side, battery box built into it. The drain plug (704) is on the left side of the bike on the side near the bottom of tank.
The oil filler neck is shorter than the -80 tank and is hidden behind a removable cover which also hides the battery.
The frame has welded on hooks to attach the cover up top with a screw on the bottom into the frame.
The left side is exposed without a cover and has a “Made in USA” transfer emblem in the center.

Capacity: It's not clear what the actual oil amount is for the tank.

1979 owner's manual 99466-79A page 6: oil tank = 3 quarts
1979 service manual 99484-79 page 1-1: oil tank = 4 quarts
1979 service manual 99484-79 page 3-2: “…oil tank capacity is 3-3/4 quarts
1985 service manual 99484-85 page 2-1: 1979 oil tank = 4 quarts
Actual capacity of my 1979 including filter change when bike is sitting nearly level:
Two quarts, start engine, shut her off, then add maybe ~8 more ounces to get to the top of the fill line.
I can add more if it is on the side stand, but obviously that's a good way to make it over flow when I stand the bike up straight. ¹⁾

The 1979 XL/XLCH owners manual (99466-79) shows a pic of a sight tube on the left side of the bike on the front edge of the oil tank.
But that is actually standard equipment for the 77-78 XLCR. The 79 frame is not the same as the XLCR frame although similar in production.

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Oil Tank Cover Mounting Brackets on the Frame:
The 80-81 frame will not take the 79 cover.
The 79 frame has welded on tabs for that cover (third pic below) , and a welded in place nut for the bottom mounting bolt, that the 80 frame does not have. ⁷⁾

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Triangle shaped side, battery box built into it. The drain plug (704) on is on the left side of the bike at the bottom.
There is an extra mounting tab welded to the top inner side of the tank in front of the vent nipple.
An “L” shaped bracket (66279-80) is attached there that is slightly curved on the end with a pad under it as a hold down point for battery.
The left side is exposed without a cover and has a “Made in USA” transfer emblem in the center.
The oil filler spout is higher up on the 80-81 than the 79 tank and the right side cover (66601-80) has a molded cutout to go over the spout and also exposes the battery.
You can check oil level and fill the tank without removing the cover.

Capacity: 4 quarts

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The battery sits on the tray that is welded to the oil tank.
Bracket (66279-80) is what bolts to the extra mounting tab welded to the top front side of the 80-81 tanks.

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79-81 tanks are 15” between the hole centers. ¹⁶⁾

Mounting tabs repaired on a 1980 frame:
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Here is a mock-up of a 79 tank in an 80 frame.
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