That bike I would say is a Buccaneer, or the closest thing to one. Thats what they called them mid 70's anyway. The buccaneer was the larger engine and fully loaded model which shows on yours with the light mount, lighted engine etc..
this one was listed on ebay earlier this year and was a very nice example:
I don't know the part numbers for the belt, and if nobody comes forward with that I would say look up the comet belt sizing charts and try to find something there. It will most likely cross with a TC88 belt but you need to measure the closed halves to see if its 5/8" (tc88) or 3/4" (20 series) and that drive system should be symmetric (V shaped halves).
When you confirm the width needed, then measure the overal dia of the rear pulley/driven it will be closer to 6" or 7" , then measure center to center on the driver and driven shafts. then you can use the charts to hopefully find a belt that will fit the bill. Once you figure that out you can usually google the various part numbers that they supply for that belt in the chart to price shop/availability through different vendors. Hope that all makes sence, I'm not the best at explaining things like that, but you can pretty much find all that info on this site linked if you search around a bit in the comet sections:
https://www.gokartsupply.com/beltchart.htm
That same tank was used by many vendors, the first few years they were steel tanks and used on ARCO, Powerdyne and Sensation mostly, by the Bushwacker and buccaneer era they were doing them in plastic and companies that still survived the mini bike crash in late72-1973 still used them Bird and Arco mainly but there were a few others I think, they dont pop up all the time, but they are out there.
If that engine has numbers stamped across the top of the shrouding running parallel with the head bolts, can you post them up?? sometimes there was a little tag with numbers that was held on by a sidecover or valve cover bolt instead of the shroud stamping so if stamping is not on the shroud maybe look for that. that would verify size of engine and born on date.
