I had forgotten that I sent a letter to Mr. Rikhye; here is what I said about the Persian Army
I have obtained a copy of Richard A. Stewart's Sunrise at Abadan: the British and Soviet Invasion of Iran, 1941 (Praeger, 1988). It has information on the Persian Army on Aug 25, 1941 as follows:
1. Guards Infantry Div (Teheran, Baghe Shah Barracks) B/G Karim Aga Buzarjehehri
2. Guards Infantry Div (Teheran) M/G Naghdi
3. Infantry Div (Tabriz) Gen Matbooi (had 8500 men incl an engineer bn)
4. Infantry Div (Rezeiyeh) M/G Ali Moini
5. Infantry Div (Kurdistan) M/G Hassan Moggadam
6.Infantry Div (Ahvaz) cdr? (Khorramshar, Abadan, Khuzistan, Bandur-i-Shahpur) included 1000 sailors at Khorramshar under Adm. Bayandor, a brigade of the 6. Div incl 45. Infantry Rgt, elms. of 1,2,30 Infantry Regiments, 8 medium tanks, 8 light tanks, 10 armored cars
9. Infantry Div (Meshed)cdr? two infantry, two cavalry rgt (Meshed), one cavalry regiment (Bojnora), 28. Infantry Rgt (Torbat), three batteries each of 75mm and 105mm howitzers
10. Infantry Div (Gorgan) Col. Mutazedi (acting)
11. Infantry Div (Rasht) cdr? (included 36. Infantry Rgt under L/C Iranpur)
12. Infantry Div( Kermanshah) B/G Puria
15. Infantry Div (Ardabil) Gen Gaderi (included two infantry regt incl 11., had 20 light and 15 heavy trucks)
17. Infantry Div (Khvoy) cdr?
Non-divisional units included the Mechanized Brigade (Teheran)
Regiments included in the above divisions were the 1. Pahlavi, 2., 11., 17., 28., 30., 36., 39., 43., and 45.
The only cavalry regiment identified by number was the 23., at Gonbad-i-Kavuz under Col. Hanjanus
It looks like a safe bet all the infantry and cavalry regiments were numbered consecutively, 1-45 and 1-25