Serial Number A748383 is coming up as an MERCURY CANADA 70 ELPTO Model Number 10704129C
70-H.P 1989 ELPTO US Serial Number Range C100000 - UP / CANADA START SERIAL # A742531 = 1989... <No question on the year model in my findings.
E = ELECTRIC START
L = LONG SHAFT (20")
PT = POWER TRIM
O = OIL INJECTION
Since your Model number 10704129C isn't coming up to help ensure a correct parts guide I was able to locate 3 others that are close enough that will work for your part searches all from the 1989 year models... If you search online the 3 model numbers below you'll find a few options to choose from...One is linked as an example.
70 [ELPTO]
10704129D
https://www.crowleymarine.com/mercury-outboard/365.cfm?mdl=TEIKSF
1070412GC
1070412GD
OEM Service Manual part number 90-13645--2 covers engine models,
70/75/75 Marathon/75XD/75 Sea Pro 80/90 (3 Cylinder) 1987 thru 1993 AND 100 & 115 (4 Cylinder) 1988 thru 1993
(U) 0A997142 thru 0D283221 (B) 09502135 thru 09793576 (C) 0A722297 and Above
(U) 0B209468 thru 0D283221 (B) 09523034 thru 09793576 (C) 0A731673 and Above
https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=90-13645--2&_sacat=0