I'm looking around and from the War Thunder (I know, I know I know) forums at:
https://forum.warthunder.com/index.p...d-the-type-74f
claims that the Type 74D with thermal sleeve on the gun was introduced in 1987.
Regarding ammunition:
It appears that the L28xx family of ammunition by the UK was also German DM13 under license.
https://en.wikipedia.org/wiki/Royal_Ordnance_L7
IOC for L28 ammo was 1959; so looks to me like you could use the following base guns for the Type 74 (with adjustments)
UK OBAT 007 Weapon 095 -- 105mm L7 UK59
for initial Type 74 IOC with L28A1 APDS and Type 75 HEP.
US OBAT 012 Weapon 098 - 105mm M68 78
for 1984 onwards Type 74 with M735 APFSDS built under license in Japan, but keeping the Type 75 HEP/HESH warhead from UK OBAT 007 Weapon 095 -- 105mm L7 UK59; resulting in the following values:
(see attachment)
Germany OBAT 044 Weapon 99 - 105mm L7 WG81
for 1993 onwards Type 74 with Type 93 APFSDS and Type 91 HEAT-MP. (It appears Type 91 HEAT did not enter service until 1993. I guess Japan waited until both rounds came into service to upgrade their ballistics computers with the drag values.)
The estimated 414mm RHA @ 2,000m given in some sources for Type 93 APFSDS is very close to the penetration given for DM13 in 1979 (220mm RHA @ 2 km @ 60 deg = 440mm RHA); so it makes sense to just use DM13 values.