[V]

oops, haha, i meant to say flexplate, not flywheel. there should be a ext balanced flexplate for a 700r4 available at a reasonable price. lemme go look now...

the 400/th350 flexplate MAY work IF a 168 tooth flexplate will clear the case/bellhousing of the 700r4. i know a 168t will not fit in an f body T5/t56 bellhousing. but since gm used the 700r4s on other vehicles, it may be bigger to clear a 168. If it does clear the housing, then you need to see if the convertor bolt pattern(3 bolts) will match up with the 700r4 convertor. If not, then you need to get a new flexplate with External balanced and the proper TQ convertor bolt pattern. 168t versions are available for under 50 bucks or so, but you need to research if a 168t will fit in the 84 700r4.