There are no torque specs for the motor mount bolts in the 57-78 FSMs.
And there is only one spec in the 79-85 FSM (rear motor mounting bolt-nut: 16 to 24 ft lbs).
For the rest, there is a “General Fastener Tightening Specifications” chart in the 70-78 and 79-85 FSMs. ¹⁾
It lists general torque values for bolt types but not specific mounting bolts.
It also says to torque to these values given in the table unless specified otherwise.

²⁾

Bolt size	SAE 2 74,000 psi Low carbon	SAE 5 120,000 psi Medium carbon heat treat	SAE 7 133,000 psi Medium carbon alloy	SAE 8 150,000 psi Medium carbon alloy	Socket head cap screw 160,000 psi High carbon quenched tempered	Socket head set screw 212,000 psi High carbon quenched tempered	Studs
#6	-	-	-	-	-	9 in/lb	Use SAE 2,5 and 8 values when grade is known with nut and sufficient strength
#8	-	14 in/lb	-	-	-	16 in/lb
#10	-	22 in/lb	-	-	-	30 in/lb
1/4“	6 ft/lb	10 ft/lb	13 ft/lb	14 ft/lb	16 ft/lb	70 in/lb
5/16”	12 ft/lb	19 ft/lb	25 ft/lb	29 ft/lb	33 ft/lb	140 in/lb
3/8“	20 ft/lb	33 ft/lb	44 ft/lb	47 ft/lb	54 ft/lb	18 ft/lb
7/16”	32 ft/lb	54 ft/lb	71 ft/lb	78 ft/lb	84 ft/lb	29 ft/lb
1/2“	47 ft/lb	78 ft/lb	110 ft/lb	119 ft/lb	125 ft/lb	43 ft/lb
9/16”	69 ft/lb	114 ft/lb	154 ft/lb	169 ft/lb	180 ft/lb	63 ft/lb
5/8“	96 ft/lb	154 ft/lb	215 ft/lb	230 ft/lb	250 ft/lb	100 ft/lb
3/4”	155 ft/lb	257 ft/lb	360 ft/lb	380 ft/lb	400 ft/lb	146 ft/lb
7/8“	206 ft/lb	382 ft/lb	570 ft/lb	600 ft/lb	640 ft/lb	-
1”	310 ft/lb	587 ft/lb	840 ft/lb	700 ft/lb	970 ft/lb	-