Date of manufacture is 1977. It is either a 99C or a 99CD. The CD had the monte carlo stock, sling and a medallion in the grip cap. Otherwise it is just a 99C. The bases you have are fine, but you might have to change your rings. Medium high rings will work fine, I believe with the low rings the largest objective you can install is either 36 or 38 mm. I have a burris 2x7x36 in the low profile rings and it is very nice. For the caliber my suggestion would be go with the slightly lower power scope and the lower rings as it makes the rifle a little more compact. It is not like you will be taking 500 yd shots with a 243! Good luck.